Or rather would, if only Microsoft made a compelling reason for Joe User not to just disable it. I run it on all the time, my Dad would probably disable it and then cry when he got hit by a drive-by installer from his browser which trashed his machine and start a rant about how poor an OS is because he thought it was the most secure version yet.
Unfortunately until people (and this goes for developers as much as users: why should an application require full administrative access in order to run?) get out of this "I know what I'm doing, I run everything as root" mentality then UAC is pretty much useless.