The User Account Control is not only about technology or security, but also about good breeding. As developers we would like not to have face with security problems, works every time as adminsitrators and work without any security checking. As end users we would have a secure system wihout having to say yes or no for anything we do with our PC.
But the world is unsecure by design and everytime we connect to Internet we are potentially subject to some kind of attack. What is our gate to Internet, most of the time is Internet Explorer. Under Vista the UAC has a big influence in IE7 as explained by Sharath. Maybe the current usability of the UAC is not perfect but disabling it is even worse. And if you really want to be safe at 100%, unplug the network cable and remove any CD/DVD/Diskette driver from your pc :-)