This is one of those "how to market a product effectively" examples that's been kicking around in my brain for a while, I thought I'd share it. About half a decade ago, Microsoft implemented a technology called Volume Shadow Copy, which maintains old versions of your files (or the difference between the current version of a file and its past revisions) so that you can restore past states for a file if it gets corrupted or deleted.
It's a smart, automatic way of doing backup, and takes smart advantage of the fact that disk storage space is so cheap. The user interface for enabling Volume Shadow Copy on a Windows 2003 machine looks something like this:
In the upcoming Leopard version of OS X, Apple has introduced a similar feature. In Apple's case, it's called "Time Machine" instead of "Volume Shadow Copy". And while I strongly recommend that you check out the Apple's own marketing for the feature, you can probably tell the whole story from the screenshot of Apple's implementation of the same feature:
Now, the whole starry-background thing is way over the top, to the point that it's off-putting. But Apple will get credit for innovation for a feature that Microsoft shipped almost half a decade ago. And they'll deserve it.