Michael Howard has a funny entry on his blog that sounds really known to me, just the short excerpt out of it:
http://blogs.msdn.com/michael_howard/archive/2007/02/08/uac-bs.aspx

Xx: What's new? Things going well with you?
Me: Excellent, we shipped Vista. Yay!
Xx: It’s ok.
Me: Waddya mean?
Xx: Too ‘noisy’?
Me: Waddya mean?
Xx: too many pop-ups.
Me: Like what?
Xx: UAC stuff
Me: When do you see the pop-ups?
Xx: all the time
Me: When?
Xx: When I do stuff
Me: Like what?
Xx: everything!
Me: like when? I probably get two prompts a day – and that’s only ‘coz I do geeky stuff. Gimme specifics
Xx: like right when I logon
Me: we suppress prompting on logon/startup, and fail the app load, you will see no prompts as you logon.
Xx: oh.
At this point Xx had a sheepish look...

Perception != Reality.

That's exactly what I hear a lot: Many complaints about UAC, but if I drill down on specific examples... nothing! 
I have the feeling that there is a lot more noise about UAC, then from UAC!
Of course this is a version 1.0 implementation, but we have done a lot of optimization just to get the right balance between security and usability.

Urs