Also, I don't understand how a car would be more trouble than it's worth? I don't mind switching my insurance, getting a Massachusetts plate, and getting a Cambridge parking sticker. I also don't mind paying $150 a month to park it off-street on someone's driveway or something (I pay that much now). So what other trouble would there be?
That's a fair amount of trouble right there. You may want to add to that paying for public transportation anyway, since parking at HLS sounds basically nonexistant, and generally having trouble parking at a lot of the interesting places that you go.
But overall I'd say whether or not you want a car in Cambridge is a very individual decision. For me, it would be insane, but then, I'm pretty eco-concious, like the exercise of walking, am used to the cold, and don't mind a bit carrying groceries a mile or so. Plus, money is an issue for me (and having a car in cambridge is a big expense), and I really loathe having to circle around looking for parking, worrying about tickets, driving in heavy and agressive traffic, and getting lost while driving, etc.
For some people, convenience and flexibility are a lot more important, money is less of an issue, and driving/parking in Boston isn't as stressful. I don't think there's any one decision that's clearly right for everybody.