Also, a new feature of Windows 7 (actually I think it first appeared in Vista) is Win-Tab. It is like alt-tab, but gives you a preview of the windows instead of their icons. If you really need to see what a window looks like while switching through your windows, that's the way to go. I don't care for it, as it's a bit laggy, but then so is Mission Control on my Macbook.
Unlike OS X where a really good Taskbar implementation cannot exist, I can add something just like Expose to Windows. It's called Switcher and it does pretty much everything Expose does.
The Taskbar is still better though because it's always there and at a glance I can see what's running.
And, perhaps most telling, the taskbar icons don't bounce around like a 2 year-old on sugar to announce that they need your attention.
OS X is basically rigid where Windows is flexible.