MOTM

I'm with Andre, Jason, and Ben in that I prefer email discussion 
lists to forums. A forum has higher "friction".

Forums do have some advantages, as John Rice said. In actual use, 
though, the categorization does not hold up. The topic of a thread 
usually deviates from the title (subject) assigned to that thread -- 
just like with email lists, but it's worse when it happens in a forum.

Forums are never as organized as they are supposed to be. Email 
lists, of course, don't even pretend to be organized. ;-)  But, with 
email lists, it's easy to scan through every message. Serendipity favors email.

It might seem that a forum is better for archives, but in reality you 
need a good search feature for a forum or an email archive. For truly 
archive-worthy reference material, a wiki is a better solution, anyway.

Whether you switch to a forum or not, I suggest that you add a wiki, 
too. (With a password that's given on request to keep out the spammers.)

John