You've got to hand it to the PHP folks when it comes to forums...
One thing that I've noticed in terms of forum/bulletin board applications being developed and used all over the WWW - phpBB is annihilating all other platforms and products, as far as being out in the market. Obviously, the nature of it being based on PHP and free. In fact, I've seen people become so accustomed to the phpBB style of navigating through messages, requiring membership to participate and adding in handles and avatars that they get totally lost when using forums or a BBS from any other platform.
I know of several such ASP 3.0 apps, I can mentally recall a handful of forums based on ASP.NET, and I may have even run across a JSP-based BBS, even though I can't immediately recall exactly which one.
But the number of forums based on phpBB are legion. There are even forums about the forum.