Mine (in order of importance):
#1 Be able to identify, instantly, new posts, new threads, go straight to the last post I read in any thread. For instance, one forum I use has a button for all new posts since last visit, or all new posts in subscribed threads - and you're automatically subscribed to any you post in, till you unsubscribe. Although I prefer this system.
#2 Excellent search function - but not over-complicated. Did I read something about 'fuzzy' searching? Keep it efficient but simple.
#3 I do NOT want to see unnecessary autoquotes from Newsreader readers. If you can achieve NNTP access, very good - a lot of people will see this as essential - Len Hewitt for one, I believe? But don't let it clutter the forum interface.
#4 Minimal but clear identification of Adobe forum hosts/employees vs regular users.
#5 Clearer road-map for newcomers so they can find the forum they need straight away.
#6 A way to ban incorrigible abusers - wielded by Oz! or a small select band of equally reasonable people, NOT the power-mad few. Even a 'vote-off' mechanism?
#7 Don't need avatars, don't want signatures except minimal signalling, as above. But if you must ... keep it tiny, don't devote one or more columns to reams of non-essential stuff like the last attempt, so a one-line post can take up a lot of vertical space, just because of the fluff.
#8 Easier text formatting for those who can't get their heads round <b> etc.
#9 Allow uploading of images, again for those who can't easily work out how else to do it. Automatic expiration after about 2 weeks?
#10 No unnecessary decoration, keep it as clean as humanly possible, allowing maximum space for the actual text of the posts. It's like Flash intros - it might look very impressive first time you see it, by the second visit it's an annoyance.
#11 If possible, css rather than table-based to keep the code load down, improve speed. cf most blogs.