I hear ya there.
At work, I've got a few users who have Vista. Company policy is that UAC must be turned on. So after a week of Vista, what are they doing? They've learned to "click-through" the UAC prompts so quickly that they don't even see what they say -- they just approve without thinking about it.
It's a perfectly natural reaction. But it's a disaster, security-wise.
That's too bad. You'd think that with good enough firewall at the server and an antivirus that automatically checks downloads and emails, etc., you can get away from UAC. UAC is needed by people who do stupid things. Maybe in a big company you have to assume you have a few of those, but it sure penalizes those who know what they are doing, and, like you mention, doesn't help much anyway, as people get used to clicking no matter what.