Dashboard

Dashboard is just awesome. Always there when you need it, but because of how it's designed it never clutters your workspace. You can set it up with exposè to bring it up with a certain button. It uses these mini-applications called "widgets." They've also been adopted by others such as Google and so on. To the extent of my knowledge the mac was the first to use them, however.

You can browse through an extensive library of widgets. There's lots of useful ones, and even more that were made just for fun by crazy people. If you're looking for a quick solution, chances are there's a widget for it. There's all sorts of things, from egg timers, to virtual pets, to... a wall? wow... ooh! Final Fantasy quotes!! uh... I mean... final fantasy ...ew (aww, stupid broken link...)

Anyhow, dashboard uses some unnecessary resources, so if that's a concern, you might want to do a little more research in that regard. However, other than that I don't see what anyone would have against dashboard.