Well... I have a particular view on UAC...
First of all, UAC is intended for "unexperienced users" that use windows... you know, the typical guy that just chats, check emails and post things on facebook... and does some stuff on office... this kind of user is not aware about system security or how to "keep himself secure" from attacks, so, to avoid that kind of infections -wich, at least in my country, are the MAIN reason why everyone has virus in their PC's- Microsoft decided to add this control... if you see this closely, is similar to the Linux kernel protections... when you run stuff with your own user, but you always need to invoke the "super user" to add programs, updates and stuff, so you need to give permission to Linux to contiue... UAC is based on that... Is new for many users because they were always on windows and never had to test a Linux enviornment... basically now you need to give permission to windows for doing "X" action, if you are unsure or you know that is not trusable, you can cancel any action before it harms your system.
If you think you have good protection (good anti-malware) and the sites you visit are secure, and you dont instal anything what you see... you can turn UAC off... anyway, I only recommend this for experienced users... you must know what you are doing.
Personally, I know what I do, but it doesn't botter me to have UAC on... if you think UAC is annoying, you never used Vista then... there IT WAS a pain in the a**... at least in 7 is quire reasonable how it works.