Here's my first annoyance (I addressed it in another thread, but repost it here for the sake of pooling.)
Because the volume of posts is so much higher on A2K than it was on the beta tester site, some settings that were appropriate over there make it hard to keep track of the topics that interest me. I'd like to have a variant of "My Posts" that's organized thread-by-thread rather than post-by-post. That way, I have an overview over all the threads I posted to.
In this context, I' like to second a remark that DrewDad made somewhere else: It would be nice if thead-by-thread lists included the name of the last poster along with the time of the last post, as they did on the old site. Call me a chauvinist pig, but I feel a stronger urge read and respond to some posters than others.