I have the twenty Ten theme, and one thing I cant do that I think would be nice to be able add drop down lists to the top of the page.
for example rather than have recent posts to the right of the feed,drag it to the top of the page, so people click on the top menu and get show the list. I also have a list of helpful webpages, at the moment there are hidden as they are half way down the page, it would be nice to add them to the top next to the "home" tab.
So rather than just have side menu and footer area for widgets, also have the ability to add them to a header area, that included the home tab and any pages you have created.
This allows you to display a lot more of the dynamic info to a visitor to you page, with out them having to scroll.
Cheers and a great theme :)