Windows Vista, UAC and Security - One Year later

Factual Questions
1

So now when Microsoft has sold 100 million Windows Vista-licenses, and the operating system has been out for over one year, one should be able to evaluate the effects of User Account Control on security - one of the major differences between Windows Vista and Windows XP.

Doper,
do you have any real world experience, first or second hand, where UAC has blocked malicious code (which is not the only, but one of the purposes of it).

Hacker,
or security expert w. code writing skills, do you (theoretically or practically) find Vista’s UAC an obstacle in your endeavours?

Also,
have there been any professional evaluations of the effects of UAC on Vista, for instance comparing security issues the last 12 month w. those of Windows XP?

I,
system administrator with Windows Vista in production for 12 months. My interests in above questions are as a professional only, and they are factual. No personal opinions, please.

2

As a sysadmin you should know that MS allows corporates to downlevel licenses, so most of those licenses are most likely used at the moment for XP. My last site was about to do a big rollout of XP. Those license sales would count as Vista licenses.