Transcending the material plane: how do you GM online?
Long story short? I don't. Period.
I'll play board games online--I've recently been on a kick, playing Sentinels of the Multiverse with several of the other members of the Greater Than Games forums--but I don't play RPGs online. I don't really feel any animosity for those who do, but it's not for me.
Why, you might ask? In my eyes, rpgs are an inherently social activity. There's something to be gained not just from the interaction of players at the table, not just in terms of collaborative storytelling but also in terms of table banter and personal relationships. Online gaming, whether via typing or a voice-chat utility, loses the inflection and nuance of face-to-face interaction. While it can be convenient, it's a poor substitute for the real thing. Since I haven't been at a lack for face-to-face gaming in quite a while, I don't intend to change anytime soon.
So, yeah...no online gaming for me. I'll stick to my face-to-face Friday night group and my yearly convention circuit, thank you!