So far there's no known upper limit to what it can't support. Idealy though, you're only going to be limited by the ammount of space and bandwidth your host allows for. In theory, it's infinite, but so far I haven't seen anyone complaining that they have too many discussions or users where things were getting bogged down.
infinite was my thinking too, lech.....with the only limitations brought on at the hosting end of things.
it is such a lean and awesome script..............I was saying to friends this morning, that I haven't seen anything this good even for sale commerically.