The wordpress software is growing. Today on photomatt's site, the lead developer of Wordpress, he announced bbPress, a simple web standards focused forum script.
The software is currently running the Wordpress support forum found here: http://www.wordpress.org/support/
It seems very fast and anyone looking to integrate a forum with their wordpress site should look at this.

Matt said this about the software
[quote]bbPress is not and will not be right for everyone. There are open source traditional forum packages, like PunBB, that get a lot of things right and push the envelope in interesting ways, so that’s covered. bbPress is not going to have avatars, or put post counts next to your name, or give every user 80 options about how they want their dates formatted, and for some people (maybe most people) that just won’t work. However even if WordPress.org is the only site that ever runs this software, it’ll be totally worth it just to get the forum technology growing again and create a richer support experience for the WP community.[/quote]

I'll be watching this software. It might be useful for future projects.