For those that haven’t checked it out yet, Growl is a notification framework for OS X. Now, that sounds really dull when you put it like that, but actually it’s an interesting interaction/interface development. Basically the theory is that you want some subtle notification of information, but not have to change applications or be bashed over the head with it. It’s a very subtle approach and you’ll find you’ll use it all the time. It’s a bit like Exposé - so obvious it’s not intrusive, that’s what makes it a radical leap.
(The screenshot above is from Growl Clock - it’s just about to fade offscreen again, it doesn’t just hang around unless you tell it to).
While you are at it, download and get friendly with Quicksilver too. It will change the way you work on the Mac forever more, especially if you have a 12" laptop.