Ordinarily, I'm firmly in the "Meh" camp about this, as even in the Vista days I always had UAC disabled since it's nothing more than an uninformative busybody. If it doesn't tell you exactly
what something is trying to access (unlike decent firewalls, etc which will reference down to an HKEY itself), then it's pointless as not only is the user left
completely uninformed, but neutered by abstract (and mostly irrational) fear.
Thus, UAC is laughable.
That said, after my recent exploration of
writing to x2 process memory space (especially with regard to utilising cross-account
SeDebugPrivilege), I must admit that I was somewhat surprised at just how easy this is to do, once you're wearing the right size ballet-shoes.
I haven't bothered to formulate any real thoughts about its potential, but (unlike most things) it has sat in the back of my head for the last few weeks tickling my more perverse inclinations of civil disobedience.

(I wasn't just a
little surprised, I was
very surprised at the sheer simplicity of it.)
Like most things from MS, UAC really wasn't very well thought-out.