What is the role/function of the Deacon in the Orthodox Church today?
Depends on who you ask, and when you ask. Since the question is in Liturgy:
The Deacon is essentially a communicator between God and the people, and between the people and God, like the angels. He leads the people in prayer to the Lord (people -> God) in the petitions, gives directions for prayer (God -> people) like "bow your heads," brings the prepared gifts to the Church (people -> God) in the Great Entrance, and brings out and distributes the precious Body and Blood of the Lord (God -> people). As agents between God and man, they also serve the Bishop, who stands in the type and place of Christ
when present in the Liturgy.
Some of these roles are muted in some way (e.g. in ancient days the Deacons were the ones "entering" at the Great Entrance, not the Priests; many times now the deacons don't distribute communion even when present and serving). Some roles are distorted (e.g. some folks assume a Deacon should only serve with a Bishop present) by some. But, sadly, most frequently the role simply isn't present (the shortage of clergy, combined with the low level of giving to the Church, means that most parishes are desperate for priests and, thus, few remain deacons for very long).
Hope this helps. If you want more information about extra-Liturgical roles, we can discuss that, too.