I can't entirely write it off as God does work in mysterious and I have no idea what's happening to these people when these things happen. What's your opinion?313 Azusa Street, AD 1900 -from whence the entire modern tongues movement sprang All major modern Pentecostal and Charismatic trajectories descend historically from this location/event.
On closer investigation of the actual phenomena (e.g. academic ethno-linguistic, historical, and neuro-biological -see below), and considering the actual problematic history of the origin of what have become standard paradigms of the phenomena within the movement itself, it becomes far more difficult to deny strong warrant for a very deep skepticism re. the vast majority of what is passed off as glossolalia in contemporary Protestantism, IMHO.
The modern tongues movement essentially began 7:00 p.m. on New Year's Eve of the year 1900, and mushroomed due to a series of newspaper articles that were initially more interested in the fact that blacks and whites were, under the direction of black pastor William Joseph Seymour who spearheaded the phenomena, having tiny joint services (which didn't last long -major branches, e.g. the Assembly of God denomination, began as an early schism of the same movement by those who wanted whites only, a sordid origin which AOG formally repented of -thank God- as a denomination not very long ago). The first article stimulated crowds of gawkers to arrive the very next day, which crowds brought even more reporters to comment, and a media series developed even more gawkers(!).
When the turn-of-the-twentieth-century Azusa street revival -the origin of the modern tongues movement- all the participants believed they had received the gift of speaking in actual extant human languages that would usher in the last day revival when people in would hear the Gospel uttered by foreigners (American Californians) in languages the Americans did not actually know how to speak; after the predicted soon coming mass supernaturally ushered revival would come the end of all ends -the Book of Revelation would soon read like a current newspaper account.
Accordingly, many of the original Pentecostals sold possessions etc. in order to travel by sea and by air, to many foreign countries, fully believing that when they spoke in tongues their hearers would supernaturally hear the Gospel (oops #1). When that expectation did not materialize, and only at that time, the chastened and to a tragic extent travel-weary movement as a whole adopted the "standard" interpretation (i.e. -as Protestant F. F. Bruce might have it, the "soon-to be traditional" modified interpretation) that the gift they had received must be some kind of angelic language, or some kind of prayer language no person but God really understands. On the surface the revised account might seem less susceptible to the sort of serious falsification the "first wave" paradigm encountered; as it turned out, however, this would not be the case.
That modern tongues speaking probably isn't a language of any kind -angelic or human- was fairly well confirmed by a massive 5 year long multi-national linguistic analysis of tongue speakers from different cultures and language groups which confirmed not only that the tongues being spoken in the movement did not correspond to any known language, but, further, that the specific manner that people "spoke in tongues" was in accordance with the phonemes (basic vocalizations) which occurred in a given speaker's native language! The "heavenly language's" origin seemed to be of the earth, not just of the earth, but regional earth locations, varying very specifically by limitation to the specific language sounds known from birth by the given tongues speaker, varying according to one's native language and place of residence.
I. Howard Marshall, commenting on the skepticism-inducing nature of the exhaustive linguistic studies, nevertheless pointed to an example of a Marxist revolutionary and atheist known to Marshall who was converted to Christ after hearing his own daughter speak in a language that he had mastered, but that -he knew- his daughter was unable to speak. Marshall felt this case too convincing for him personally to discount despite the movement as a whole being still, well, entirely unconvincing to him (note, despite Marshall showing no bias for cessationism).
To sum up, I have never thought scriptural arguments for cessationism by Protestant cessationists are even remotely convincing (see Addendum 2 below), however the nature of the phenomena in question themselves when placed under closer scrutiny (not to mention ancillary issues like heretical Sabellianism/monarchial modalism espoused by millions of pentecostals, e.g. United Pentecostal International et al, God wants you rich if you donate to me Prosperity Theology which is very prominent throughout all Charismatic and Pentecostal trajectories) and... well... just color me deeply skeptical of at least the vast bulk of the whole contemporary movement for now -while being anything but a cessationist personally.
Addendum from the Wiki article on Glossolalia
Substantial scientific studies have been published that provide an objective description of the linguistics of glossolalic speech and the neural behaviour of the speakers.
Linguistics of Pentecostal glossolalia
William J. Samarin, a linguist from the University of Toronto, published a thorough assessment of Pentecostal glossolalia that became a classic work on its linguistic characteristics. His assessment was based on a large sample of glossolalia recorded in public and private Christian meetings in Italy, Holland, Jamaica, Canada and the USA over the course of five years; his wide range included the Puerto Ricans of the Bronx, the Snake Handlers of the Appalachians, and Russian Molokan in Los Angeles.
Samarin found that glossolalic speech does resemble human language in some respects. The speaker uses accent, rhythm, intonation and pauses to break up the speech into distinct units. Each unit is itself made up of syllables, the syllables being formed from consonants and vowels taken from a language known to the speaker.
It is verbal behavior that consists of using a certain number of consonants and vowels[...]in a limited number of syllables that in turn are organized into larger units that are taken apart and rearranged pseudogrammatically[...]with variations in pitch, volume, speed and intensity.
[Glossolalia] consists of strings of syllables, made up of sounds taken from all those that the speaker knows, put together more or less haphazardly but emerging nevertheless as word-like and sentence-like units because of realistic, language-like rhythm and melody.
That the sounds are taken from the set of sounds already known to the speaker is confirmed by others: Felicitas Goodman found that the speech of glossolalists reflected the patterns of speech of the speaker's native language.
Samarin found that the resemblance to human language was merely on the surface, and so concluded that glossolalia is "only a facade of language". He reached this conclusion because the syllable string did not form words, the stream of speech was not internally organised, and– most importantly of all– there was no systematic relationship between units of speech and concepts. Humans use language to communicate, but glossolalia does not. Therefore he concluded that glossolalia is not "a specimen of human language because it is neither internally organized nor systematically related to the world man perceives".
On the basis of his linguistic analysis, Samarin defined Pentecostal glossolalia as "meaningless but phonologically structured human utterance, believed by the speaker to be a real language but bearing no systematic resemblance to any natural language, living or dead".
Practitioners of glossolalia may disagree with linguistic researchers and claim that they are speaking human languages (xenoglossia). For example Ralph Harris, in the work Spoken By the Spirit published by Radiant Life/GPH in 1973, describes seventy five occasions when glossolalic speech was understood by others. (Scientific research into such claims is documented in the article on xenoglossia.)
 Comparative linguistics
Felicitas Goodman, a psychological anthropologist and linguist, studied a number of Pentecostal communities in the United States, Caribbean and Mexico; these included English, Spanish and Mayan speaking groups. She compared what she found with recordings of non-Christian rituals from Africa, Borneo, Indonesia and Japan. She took into account both the segmental structure (such as sounds, syllables, phrases) and the supra-segmental elements (rhythm, accent, intonation), and concluded that there was no distinction between what was practiced by the Pentecostal Protestants and the followers of other religions.
In 2006, the brains of a group of individuals were scanned while they were speaking in tongues. Activity in the language centers of the brain decreased, while activity in the emotional centers of the brain increased. Activity in the area of control decreased, which corresponds with the reported experience of loss of control. There were no changes in any language areas, suggesting that glossolalia is not associated with usual language function. Other brain wave studies have also found that brain activity alters in glossolalia.
Attempts to explain these physical and psychological from a scientific perspective have been suggested, including mental illness, hypnosis, and learned behaviour... http://en.wikipedia.org/wiki/Glossolalia#Neuroscience
Addendum 2 Re. Protestant "Cessationism." While the modern tongues movement invites skepticism, the questionable exegesis among Protestant cessasionists hardly suffices to inspire confidence of its own right. Protestant scholar F. F. Bruce begins his fine little book Tradition: Old and New
(Grand Rapids: Zondervan, 1970) with the example of another writer in his own cessationist denomination citing "proof text" 1 Cor 13:10 as meaning "when the perfect, -that is the BIBLICAL CANON- comes, imperfect things -stuff like TONGUES AND MIRACLES- will pass away."
The writer had described said reading as "the standard interpretation in our brotherhood." This description for Bruce warranted its place as his first example of "Protestant tradition." Bruce agrees that Protestantism no less than any other trajectory has its own tradition, however the manner in which his writer appealed to it uncritically invited the retort:
"Quite apart from the validity of the exegesis -and that the concept of the completed New Testament canon was present to Paul's mind is extremely improbable- it is unwise to refer people of independent thought to a standard interpretation, for the very fact of its being so described renders it suspect" (ibid, p. 14).