This is funny: I've only really ever used the "shake-to-undo" on the iPhone either by accident, or when it wasn't actually available (when I had to undo something, and thought the app I was using supported it). But it can be a handy feature for some, and because of that, someone (named Nate Stedman) has "ported" it over to the Mac, available for download on your laptop MacBook, MacBook Pro, or Air. In other words, install the app, and then whenever you shake your portable Mac, the accelerometer inside will try whatever Ctrl-Z does on the app you're working on, essentially implementing "shake-to-undo."
Like I said, funny. This is more of a joke than anything else -- it's not really practical to be shaking your MacBook around every time you want to undo something. But "Shake-to-undo" is pretty cheesy as it is, and it's extra silly to be flinging your device around on a bigger computer. Apple's brought quite a few iOS features over to Lion lately, but this is one that should probably just stick to the smaller devices.