I've lived in Boston my whole life. Don't have much experience with the Bay Area (beyond knowing a couple friends there and visiting once), so I'll stick mostly to the Boston side of the equation.

Boston is cheaper, but I'm not sure I'd say significantly cheaper. 1BRs start at about $1200/month here - I've heard that the minimum in Mountain View is about $1500/month. With roommates, you can get a room for $700ish/month in the Davis Square area, which is about on par or a little less than Mountain View. Gas prices are a little lower (talking pennies, though), restaurant prices seemed a little higher in Boston (though maybe my friends just took me to inexpensive restaurants in Mountain View), and I didn't get a chance to check out stores in California.

You can save a ton of money here by living away from the major subway lines. A friend of mine has $400/month rent (3 roommates) in Brighton because he's at the end of the Green Line, which is frigging slow. Another friend had $450/month (1 roommate) in a gigantic 2BR on the Newton/Watertown border. I looked at rents in the Teele/Inman square areas in Somerville; they're about $200-300/month less than equivalent apartments in nearby Davis/Harvard squares, because they aren't directly on the subway line. If you need a car anyway, definitely consider living in one of the areas that's not well served by public transportation - you'll make up for it in rent.

The suburbs also have lots of greenery, particularly once you get outside the 128 belt. It's not like suburbs elsewhere in the country, all strip malls and parking lots laid out on a grid. Typical towns in the Boston area have one or two major roads running through them, residential roads branching off them, and lots of unused space because none of the roads are straight. We're on an acre of land, extending about 500 feet back from the road, and when one of my dad's friends from Cupertino visited, his son said "Wow, you live on a park."

Driving in Boston sucks. Whenever possible, I drive into Alewife and take the subway in.

The diversity in the Boston area is a major plus. It's likely that you'll have normal friends here, the kind that think that yet another social network is just a burden and not an opportunity. There's a significant tech population, but it's not like everyone lives and breathes technology.

As for the startup scene: there's an important cultural difference between Boston and the Bay Area. In Boston, the expectation is that you'll work for an established company for 10-20 years, pay your dues, and then start a company. When I talk about startup founders I know, West-coasters seem to assume they're my age - no, most of them are parents of friends or older coworkers I've worked with.

This has been changing a bit recently, because of the general trend of younger people starting companies and the large college population in Boston. But it still seems to be the expectation among investors. Maybe someone who's sought funding more recently could comment, but when my cofounder was testing out investors, many of them seemed very skeptical. Encouraging, but not willing to part with cash for a couple guys 2 years out of school.

Lastly, I'd encourage you to go far from home. I didn't; actually, I moved back home after college, since there were no shortage of jobs in my field close to where I lived, and I could save up cash and use it to fund my own startup. Which is good, it gave me options and let me do stuff I wouldn't otherwise be able to - but now I'm looking to move out to Silicon Valley, precisely because it's on the other side of the country.