I really like the profile preview boxes, but I have to admit I didn't expect to see the trophy feature... I had looked at it under the Alerts box in confusion, but that disappeared quickly. Very nifty and fun feature; I assume that it can be extended to other things, not just the amount of posts? Perhaps uploading your first avatar, creating a signature, etc.
Overall I'm amazed. I keep finding a number of new surprises so I'm not quite sure exactly which to pick first.
Right now, it's very static criteria (>X days registered, >X posts, >X likes), but we want to do hooks to give you trophies for specific events. They have to be implemented specifically, whereas the criteria-based ones can be built by admins.
I love the floating forum descriptions. When I uploaded an avatar it was automatically resized and then I could pan the image any direction to center it within my avatar frame. THAT... is exceptional UI design.