Now, UAC is painful at times like installation (but getting better according to Reducing Elevation Prompts in RC1), however, there are loads of cool features hidden behind all the glitz of Aero that are really cool. Like Previous Versions:

It uses the Volume Shadow Copy technology already in use on Windows Server 2003, and it "hides" itself as part of System Protection / automatic restore points:

This is definitely one of those features that "sell" a product.