Well, a lot of time when I talk to people about Windows Vista, two things pop up: User Account Control and Digital Rights Management. I will save DRM for an other post but I think that there are two blog posts you could read with regards to UAC:
Jeff Jones wrote an excellent article about how he uses it: http://blogs.technet.com/security/archive/2007/02/12/the-value-of-uac-in-windows-vista.aspx
And then, if you want to get technical, it is (once more) Mark's blog that is worth reading. http://blogs.technet.com/markrussinovich/archive/2007/02/12/638372.aspx
For me it comes down to the number of pop-ups with UAC and this really has to be put into perspective: I am working as a standard user on my Vista box and rarely need any elevation at all - unless I have to install stuff (and then I want UAC to ask me for elevation). The challenge with UAC is, to survive the first few days - the time during the setup of the machine. There you get a certain amount of prompts (obviously). Once, your machine is set-up and running, well there is barley any need for elevation.