If you want to help please read this topic carefully. I decided to choose from these three options. Please don't hesitate to say what you think about it:
1. BBPress - http://bbpress.org/
OK, this one is everyone's favorite. If I remember, it was written by Matt himself so it should be WP compatible. But what about WPMU?
2. Simple Press - http://www.stuff.yellowswordfish.com/simplepress-forum/
Now I must say that I've never heard (read) someone complaining on this plugin. Does it mean that it's good or that very small grop of people are using it? All I know is that it's author did some other really amazing plugins.
3. Boonika Blog Forum
No it's not a plugin. It's my idea for a simple forum. I thought; "Why wouldn't I just create another blog, forum.mysite.com for example, and use it as support forum?". You tell me if (and why) is this a bad idea. All I know is that:
a) I can categorize all topics
b) don't have to worry about new forum versions (upgrades)
c) 'search' option is there like on any other forum
d) 'posts' can act like 'topics' and 'comments' are same as any other forum's comments
e) I could also include (gr)avatars easily
f) easy backup
That's it. Tell me what you think. Thanks.
DISCLAIMER (I had to put it here;)): This post was written by a designer (not a programmer) who sometimes only thinks that he knows what he's talking about. Chances to get a useful advice from him are are 50-50 (sometimes less).