1. Sometimes when I see a post that I'm interested in keeping up with, I think it would be good to have a way to add them to a "watchlist" or something. That way it's easier to find them again to see how the conversation is coming along and for future reference.
2. Have a link to "view new posts". I know I can find new posts on the front page, but I'm not talking about those, although it is related. What I'm talking about is a link to show every new post since my last visit. Sometimes the threads pour through so quickly on the front page, that we're left with go to each topic and finding what's new there. Sure, it's feasible this way, but takes time when compared to viewing everything in one spot. Even a "next page >" at the bottom of the front page would be helpful.
3. What about an "e-mail me replies to this post" function?
4. I like being able to view the posts I've started or replied to. Please keep that. :) However, I could be wrong, but I don't think they actually show me when someone has posted to those, do they? If not, that would be cool as well.
5. Maybe on the right, in the dark grey sidebar, you could add links to commonly asked for sites (i.e. codex, plugin repository, etc.). Perhaps you could add the latest or hottest plugin? Just a thought.