Currently in the NYC metro area, although my experience with "Any day now my social network for ABBA lovers / fantasy soccer league / Twitter/Facebook/Tumblr/Myspace/Veoh/Youtube mashup will be worth millions" programmers has in the bast encompassed people from the Boston area (Harvard & MIT), Romania, Russia, and Denmark.
SIGH as much as I am reluctant to admit it, I'm starting to realize that what people say about S.V. is true - it is THE startup hub.
But IMHO, not because of the "infrastructure" but rather because of the more open, willing, "let's see if we can work together and if not, we fail - so what? Let's try something different" attitude.
Everywhere else nobody seems to understand that it takes a BALANCED team to create anything good. Programmer's think they're God's gift ... investment bankers think they're God's gift ... VCs think they're God's gift ... MBAs think they're God's gift ...
Only in S.V. is everyone seemingly willing to put ego aside and explore new possibilities with people different from them.
I would think based on the financial success they've achieve more people would be inclined to follow ... but ... apparently not.
</sarcasm to infinity plus plus plus>