There's a guy I knew there named [link|http://blogs.msdn.com/oldnewthing/|Raymond Chen]. Total and complete asshole. If he found a bug in your department's product, he'd check out the source, write up a fix, then send the fix, diffs, and an all staff e-mail indicating what a bunch of idiots everybody in your department was for missing something as simple as what he had fixed.
I actually worked IN his department for 4 months - not something I'd want to do again. OTOH, I watched this guy read a debug stream from Wordperfect in RAW HEX and figure out exactly where a nasty compatability issue with a prebuild of Win2k was cropping up. He was most definitely NOT stupid, and he definitely had some skills.
(He was also a completely amoral antisocial git, but that goes without saying at Microsoft.)