First thing I do after a fresh install of Vista is disable the UAC.... What a huge pain in the Arse that thing is!... Ok it can be configured to not be so intrusive but even so, I'm the administrator and I certainly know what I'm doing.
In more of an answer to your question... It's supposed to pop up any time a administrative order is given or some strange software is used without a MS licence(which I might add, costs a great deal of money). Which is great if your on a network but not so much if it's just little old you at home trying to change your folder details.
Much has been written about this often hated utility and if you scour Google you'll find reams of information on it. Many say it's best to use it, personally I think it's up to the user in question..If you feel you can be incontrol of your own destiny then get rid it... But if however your thinking that some maligned peice of software is going to ambush you or your incapable of making a sensible decision keep it enabled..
You do realise this is could spark a huge debate..