As far as I can tell, I’m not the only one who has pretty much given up on bbPress, WordPress’s long promised forum app. Simple:Press is a nice alternative that installs as a WordPress plugin and lets the user configure a forum within a WordPress site.
Be warned, though — Simple Press is fairly complex to set up and has hundreds of options. For the most part that’s simply inevitable with a full-featured forum, but be warned you’ll need to spend some time with the admin interface and customizing a page template to make it look nice.
On the other hand, it’s worth it as it already does out of the box pretty much everything that bbPress may do someday if it ever really gets the attention it needs. I’ve got a test setup here, though I’m still trying to decide if I really need a forum here.