I of course had seen this before, and am not put off by it, but am curious, what is the concept behind the nearly constant signing of the cross?
Why do people sometimes touch the ground after giving the sign of the cross, and sometimes not?
I guess overall, as there is much repetition in the liturgy, what is the theology behind this?
Is it normal for the congregation to have a fairly informal attitude, i.e., wandering about, in and out, (1 even answered her cell phone waiting to venerate the cross, which I'm sure is not too kosher...)?
Crossing yourself is part of the way Orthodox pray. I imagine this is not that different from the Roman Catholic custom. Touching the ground or even bowing all the way to the ground is just part of the personal devotion of the persons doing it. There is generally no enforced uniformity in these matters. I say "usually" because in some services during the great fast (lent) you really
should do it at some times.
People do wander around in Church during services; to light candles and pray or perhaps to greet someone with a kiss after communion. I understand that this could seem informal but it is actually part of what one should do at Church.
Orthodox people are not known to be the most punctual crowd. In some Churches there are prayer services going on both before and after Divine Liturgy. This makes it hard to tell exactly when the actual Liturgy starts. In other Churches there are very specific times when the Liturgy starts but people are kind of used to take these times more as guidelines.

The phone thing is a little bit surprising. My priest would definitely disapprove, as would the rest of the participants in the Liturgy.

I'm glad you liked the experience! Some say standing becomes easier with time.

EDIT: About the repetition, I don't actually know but the Orthodox Church adheres to the
Lex orandi, lex credendi (he rule of prayer is the rule of belief). Our beliefs are contained in our prayers and these prayers are repeated so that they will "stick" in the hearts of the believers. Perhaps other posters can correct me or expand on this?