[xtreegold]

Maybe you can shed some light on this doubt I've always had:

why does the UAC need to gray/black out all the display?

It's such a mess, especially when you have more than one monitor. Is there a technical reason or is it just UX?

[jimbobimbo]

This is done to prevent malware faking the prompt and/or user consent. And it's not just "blacking out the display" - the whole thing is executed on another desktop (in OS terms, not in user terms): http://blogs.msdn.com/b/uac/archive/2006/05/03/589561.aspx