A bike sharing program is a neat idea, but actually riding bikes in Boston is a terrible experience. The roads are in bad shape, there are no bike lanes, and the drivers are homicidal.
Public transit in Boston certainly isn't bad, it's better than most cities I've lived in and it may very well be better than the valley. But the subway is generally only helpful if you're going to and from downtown. If you say live in Somerville and work in Allston, you're pretty much out of luck, unless you're willing to transfer between the bus and the subway a few times.
In general I found having a car was a pretty key part of living in Boston.