If you guys are like me, and most of you are, in that we have used Windows for most of our lives, and we are known as the "computer geeks" in our circles, I don't think things like UAC affect us one way or another. To me, it's simply a nuisance, period. It's not like I ever try to install something accidentally, and even if I did double-click on it accidentally, I'd just cancel the wizard at some point. Also, as JJ said, our comfort with computers makes us comfortable with installing a bunch of different programs to try. I don't use sandboxing or vm's. i tried at one point, but it was too much of a headache. Look, I know if something I'm installing is fishy. i don't need UAC to tell me or anyone else. I just hope that even if i do intentionally try to install something that is fishy, my AV or other security software will catch it. And it has for the most part. Some things have slipped through, as I've talked about here on the forums, but even those were due to some pretty odd circumstances.
All these things like UAC are really for the 95% of the population who are not very comfortable with computers. They don't understand the whole system, with the drivers, files, folders, program files, application data, etc. It's all foreign to them. So UAC and similar things are very good for them. But even then, i doubt how effective these things actually are. I suspect that more often than not, these messages just make people nervous and want to call their computer geek friend to check and see if they should or should not install this thing.