I'm not quite sure if I like the topic preview. It might be hard to get the desired behaviour without using a lot of code. Do many people like something like this? I usually just open topics I want to look at in new tabs.
@trickoff: The avatar uploader should be possible. I will probably take a look at it, as soon as the first features are done. I'm also not sure if it will be possible to have a jQuery UI notify widget message after you updated your password or other things in the UCP. I will need to look at this.