I have a (minor) problem with switchable graphics on my laptop (Lenovo T520, NVidia Quadro NVS4200M and some Intel, drivers up-to-date).
When I run an action on Windows 7 that requires an UAC confirmation, my screen goes black before showing the prompt, just like when changing screen resolution or something. On my previous laptop (with a single graphic card) I haven't noticed anything like this, only the usual gray shadow. That's why I believe the issue is caused by switchable graphics.
This is not a very serious problem, it maybe takes a little bit longer to show the message box (on the other hand, I find it quite slow on every machine I use...), but it's annoying.
I know that Win7 is no Linux, so I don't really expect that there is any solution, but maybe... :)
EDIT: I've found Stop UAC/Secure Desktop from dimming the screen, which solves the issue, but at some cost. I just like the screen dimmed, I don't want it to go black before it get's dimmed.
Yes, I know that maybe it's a bit over-customization, but we're at superuser.com, right? :)