Or P3B, but they are still extremely sought after. At a LAN party someone was selling one and it was gone within 1 hour.
The BX is faster than i815 but to be honest with you, If I was building a new system I would get the more modern i815 unless I knew someone selling their BX board.
By the way: If you had bought the BX about 2,5 years ago (as I did) odds are you still would be using it with a faster CPU, I never got so much mileage out of a mobo before: my P2B-F is running strong at about 1GHz.
Just think, this board lived through the entire P2-P3 era (3 years) and was compatible with almost all Intel CPUs except the new Tualatin that is IMO the best proof that the BX was a superb design feat not to be repeated anytime soon. But it is old and unless you get a board somewhere dirt cheap I wouldn't realy use it