My good buddy Jeff Prosise talks about setting up his new Vista machine and complains about the "constant badgering from the User Account Control (UAC)."
I've installed Vista on freshly formatted partitions of the three desktop machines I use (and replaced the video board on two of them), and while the UAC tends to be most active during setups and installations, it becomes virtually silent in day-to-day use. I use all three machines for writing and for WPF development with Visual Studio, and I rarely see the UAC any more. When it does pop up, I get the chance to re-evaluate what I'm trying to do.
The Mac vs. PC "security" ad is, I believe, one of the most shamelessly dishonest (non-political) commercials ever to appear on American television.