A couple of WordPress related sites you might be interested in:

WordPress MU
WordPress MU is a new multi user version of WordPress. I found the site few weeks ago and it looks pretty interesting. I am yet to download and experiment with it, but essentially it is for building communities blogs, blogs about niche subject, clubs, schools etc.

bbPress
The makers of wordpress have also created their own bulletin board software bbPress which they claim is focused on web standards, ease of use, ease of integration, and speed. bbPress can be integrated with WordPress its definitely worth looking at. I have previously used phpBB but with no coding knowledge found it incredibly difficult to try and make it user friendly for search engines.

I hope to have a bit experiment with both of these soon so will report back. If anyone else has tried please feel free to share what you thought of them.