I had to "jump in" here, since I'm Orthodox, and thought I'd join the discussion. (I've already visited the other thread on Orthodoxy, but I think RealAnastasia wants to know the "basic" differences, not a major theological discussion -- am I right?).
I converted to Orthodoxy over 10 years ago, having been a Roman Catholic for all of my life (25+ years). I think studying the IF helped me know that there was such a thing as the "Orthodox Church," but it was through a series of fortunate events that I became a member of the faith (too long of a story to tell here!).
Anyway, the first thing to remember when introducing yourself in an Orthodox Church, is to say that you are an "Orthodox Christian." If you say you're "Russian Orthodox," "Greek Orthodox," etc., those who are "cradle Orthodox" (born into the Church) will look at you like you have TWO heads! Basically, it's ALL the same church -- the only difference is the LANGUAGE. (My church is the "Antiochian Orthodox Church" -- originally from Antioch, Syria where St. Peter was their first Bishop). I've been to RUSSIAN and GREEK churches when I travel, and the Liturgy is IDENTICAL to mine, except for the language (Greek or Russian, but mostly English).
Dasha gave a LOT of great information! We just finished celebrating Easter on May 1 - the week before was Holy Week (with services each evening -- more beautiful than the one before!). Orthodox Christians greet each other at Easter (and after!) with "Christ Is Risen! Indeed He Is Risen!" (I could say this in Russian, but don't have the Russian alphabet on my computer -- let me know if anyone wants it phonetically).
Yes, Orthodox priests can marry (before their ordination), and those who don't usually go on to either serve in monastic communities or take leadership positions (Archanmandrite, Bishop, Archbishop, etc.) in the Church. My priest is married and has two lovely teenage children.
The Divine Liturgy is held every Sunday morning (no Saturday evening masses like the Catholics or others, although we do have Vespers on Saturday, which is actually the "start" of the liturgical cycle). We only have ONE Sunday service (so everyone can celebrate together).
The Divine Liturgy was written by St. John Chrysostom (Bishop of Constantiople), so it's ENTIRELY different than the Roman Catholic mass. 99% of the prayers are sung (either by the Priest, Deacon or Choir, along with congregation), and there is no piano or organ (some Orthodox churches DO have an organ - our's does not -- all acapella).
Um, what else . . .?
We celebrate X-mas at the same time as everyone else. Our greeting at X-mas is "Christ is Born! Glorify Him!"
We have all the same sacraments as in the Roman Catholic Church -- baptism, communion, confession, confirmation (called "Chrismation"), marriage, holy unction ("Last Rites" in the Catholic Church) -- I think I left something out.
When a child is baptised, he also receives his First Communion and Confirmation ("Chrismation"). Unlike Catholics whose children don't get to have their First Communion until they are 7-8 years old, Orthodox babies can receive Communion beginning at their Baptism.
I would urge anyone who lives near an Orthodox Church to go and visit. All of the Orthodox web sites in the US have search engines that allow you to type in your city, state or zip code and are able to tell you the closest church. THEN, it would be great if you "report back" and tell us your thoughts, impressions, etc.
Here are some web sites in the US. The majority of these churches have services in English AND the native language.
Greek Archdiocese:
www.goarch.orgOrthodox Church of America (Mainly Russian):
www.oca.orgAntiochian Orthodox Archdiocese:
www.antiochian.orgP.S. I invited a friend of mine to attend Divine Liturgy a few months ago. Later, he thought it was "nice, but long" (about 1 1/2 hours, but that's with over 500 people going to communion!). Don't let that scare you off!