The idea of Facebook being a place of serious religious discussion makes me feel unwell.
I had a Coptic monk ask to befriend me on Facebook a while ago. I politely declined (this was face-to-face, not a friend request on the actual website). I am sure he would have been nothing but a joy, but I do not want to start down that road. I am surprised that there are Orthodox people who do not have this a similar attitude. I can understand people of some level of authority in whatever church you're in using FB, since they are essentially public figures, but at the level at which most laypeople use Facebook, I don't see anything good coming from it ever.
I prefer forums, for a level of "safety".
I initially started using FB as a way to collect and comment (notes to self) on things I wanted to save, watch, etc. It seems I attracted attention by doing that though, and ended up with a good many friend requests.
There is less "safety" there, but I do have some friends that I trust - I do have a number of "solid" folks from AFR, for example. But then again, for lesser-known people, anyone can claim to be anything. Just because they claim to be a priest, doesn't mean they are. I have a few I have my suspicions about.
Just like in the parish though, you learn people over time. Some are always solid, and you eventually build a level of trust. Some are generally good. And a few - I know full well to disregard (and in a case or two have simply unfriended).
Overall it has been very good for me. I have a small number of very trustworthy friends who I can count on to give solid answers, and eventually was helped into a connection with a spiritual father who could answer certain issues for me (with the blessing of my priest of course - he actually wanted me to find someone else for these things). (My SF is not on FB though, but I was put in touch with him through a FB friend.)
Though more than once, because I've had a question about something there, I have brought it here for opinions. I have those I trust here as well, and when my inner voice agrees with what to accept, and what not to - along with the people I trust most (and my priest if it comes to that), then I feel better about it.