Two ideas for new features on the forums:
1. A "Mark all as read" button. I'm not sure how the code works, so I can't get more specific, but it's pretty self explanatory. Pretty useful feature in other forums I've used.
2. An "Ignore this thread" button. Would be good for users who don't want to sift through some of the garbage discussions. You could just ignore them, but this could permanently set a thread's tank icon to gray, making browsing a little faster. Might be an increase on server load, again, I'm not sure how the code works.
I'd say the first would be a lot more helpful (and used) than the second, but both would be nice.