Think... Look around your screen right now. It's okay, we'll wait.
At this very moment, applications are fighting for your attention. Between chat windows, Finder windows, Web browser windows, and everything else, it's amazing any of us can concentrate at all. As it has become easier to multitask, we've become more likely to have two dozen windows on the screen at any given moment. Innovations like Expose makes finding what you want in the sea of visual stimuli easier, but they've done little to remove those distractions.