I don't know if this has been posted, but I'll give it a shot...
I've accumulated well over a thousand bookmarks and have been much too lazy to organize them into folders. If you could automatically cluster bookmarks (http://vivisimo.com/ does this with web results) I would be eternally grateful.
One more suggestion is to learn usage patterns in a particular website. For example, when I go to http://www.nytimes.com, I generally click on the opinions sections. If the browser could anticipate that I typically go to the opinion section, it could start to preload it before I click on it.
I realize the later suggestion is much easier to implement than the former, but the clustering would be very useful for lazy surfers like me.