Looks like I'm not the only guy who has thought of jamming with other people online.
I've stumbled across a post by a guy named Brad (of Brad Sucks fame) who came across a beta version of an app which is, as he put it, Skype for Musicians. Anyway, he's actually accomplished the feat of jamming with other people via Ninjam, which was released yesterday. (Aside: The brains behind Ninjam is Justin Frankel, aka the guy who developed WinAmp.)
Since I'm still in recording mode, I've yet to get a chance to play around with this thing.
-George Ryan