Just two ideas for now, based largely on features familiar to me from Bay12 and Sufficient Velocity;
1. The ability to search for posts or threads by a particular user.
2. A single button which takes you to a search list of threads you have posted in that have new replies since your last visit.
Neither of them are very important, but the first is nice when you want to see what a particular user has been up to lately, and the second I tend to rely on a lot due to my ability to forget I've posted in a thread or which threads I've posted in (without it I tend to worry someone asked me a question somewhere and I just left them bereft of an answer).