While Hipcal is lacking in features that are crucial to me (repeating tasks, no import/export yet [!]), I really like its interface. It presents a lot of information at once, but still seems organized and tidy. Here's a screenshot:

http://argotnaut.com/screenshots/hipcal.jpg

It's easy to see a couple of days' worth of tasks (and the categories they are in) on the left side, and a summary of all tasks (overdue in red) appears on the right panel.

(One thing I _don't_ like about Hipcal is that you are forced to choose a time for tasks that have a due date.)

I'm not suggesting that you steal the interface outright, of course, but thought this might spur some ideas to help alleviate too-many-tabs-itis.