If you use OS X, this is just such an incredibly cool thing. It really is. It's the sort of thing that can change the way you use a computer.
I'm not going to claim that this will change your life, make you lose weight, fix your hair, and get a great new girl(boy)friend, but it's definitely very high on the pretty damn cool scale.
Try it, try it, you will see, you will like it in a tree.