My point is to back up what Doug says about the mixing not being a geographical problem. Boston in general and Cambridge in particular are sometimes held up as a well-heeled snooty ivory-tower lefty outpost (maybe more as a right-wing accusation) and a thoroughly gentrified one at that, and that seems to me very much not the case.
Moreover, it's struck me that whatever social-democratic threads are there are far more well integrated into the local scene than the impression I had had before I moved to the area. It's not a town vs. gown thing.
The comparison to Chicago (which has a reputation even among Mass-ians as being more "down-to-earth") is that neighborhoods seem more economically integrated around Boston, and have a higher "granularity" than in Chicago, where you have relatively huge swaths that seem one or the other. That is, there is more geographical isolation of culture there.
I'll grant that this is all impression and I have no data at hand to back it up.
-- Andy