I commute down the Beacon/Hampshire corridor in Somerville and Cambridge. That's the lion's share of my street riding on my commute. I'm lucky in that the Beacon/Hampshire corridor has bike lanes or sharrows for the entire length. It's also one of the busiest bike routes in the Boston area and cyclists, on the whole, are pretty respectful of trafffic laws as are most of the drivers. I don't know if there is a connection but the combination makes for what seems like a safe bicycle commute.
There are other places in Cambridge that aren't quite as pleasant. The stretch of Massachusetts Avenue in and around Central Square is the opposite of the Beacon/Hampshire corridor. In my experience, cyclists riding there are crazy and drivers are even crazier. I simply avoid the area although it would make my commute shorter. Somerville is upgrading Beacon Street to include cycle tracks and other cycling infrastructure. I am not aware of any plans Cambridge may have for Mass Ave in Central Square. And I'm not sure that more cycling infrastructure would make it safer - I know that there is a debate between people who favor infrastructure and vehicular cyclists who disagree with that sentiment.
Regardless of where we ride, I think we should ride cautiously. I never make the assumption that cars or bikes won't take a right turn in front of me, I never assume that cars or bikes won't race through a red light, and I don't assume a driver or fellow cyclist sees me until I see the whites of his or her eyes. The latter is how Boston driving seems to work and it is useful to incorporate that into how I cycle. I follow these rules whether I am cycling in the city or suburban or rural roads. In the city I ride much slower than I can, averaging 11 mph or less consistently. I avoid the door zone, staying to the left side of the bike lane or taking part of the car lane when no bike lane is available. I recently added a dynamo hub to my commuter and I use the daytime running lights (front and rear) on my commute. Cycling infrastructure may help but most of my cycling will be on streets without such infrastructure for the foreseeable future so watching out for myself is the best thing that I can do to ensure my safety. This isn't a guarantee but it does give me the best chance of staying safe that I can get. After all, I'm just one more person trying to get somewhere without incident.