SF is a great place to build a startup, but a lousy place to live. I never felt like I could really be myself there (despite meeting hundreds of supposedly like-minded people).
Bostonians are far less friendly on the surface, but man, you can really get to know them. People are nerdy, intellectual, informed (and not just about tech), opinionated, and largely quite sane.
The pace of the city is slower, too, in a way that I appreciate. When I go to a tech event here, I'll often meet someone and spend an hour locked in conversation with them. That kind of deep, engaged conversation never happened in SF, where people are perpetually on the go, and cutting from one thing to the next.
Outside of work, Boston (and by this I specifically mean Cambridge and Somerville -- or "Camberville" as we call it) is the best place in the country to be a nerd. The place is filled with swing dancers, LARPers, grad students, cult movie screenings, comic book and game shops, and quite possibly more CTY alumni than any other city.
Simultaneously, we've got a lot of general culture, too -- lectures, theater, good food, and so on.
Stuffy and introverted? Sure, a bit. But you can get past that quickly, and discover a wonderful place to live.