The most interesting thing about the Rodney Stark's book is that it tries to provide a sociological model for how christianity spread so fast. It suggests the idea of networking and somehow Terry is packaging this with his own opinion which does have misogynistic overtones (Terry you have to admit this is true). I'm saying this becuase I don't think Rodney Stark suggests anything misogynistic.
Rodney Starks ideas are based on assumptions and guesswork because there is no concrete proof of the numbers he suggests and he sometimes contradicts his own assumptions. However the model of networking he suggests does have merit and makes sense. I can agree that women probably networked and that this did to an extent cause christianity to increase. But then again men and women have always networked so networking is not peculiar to christianity.
I think that as others have suggested lots of different forces came together but the main engine for the spread of christianity,imo, was that the Roman empire was very tolerant and that it finally defined and assimilated christianity.
edit - Judaism maintained its resistance to Rome much more than Christianity and that is part of the reason they did not grow as exponentially. Plus they were very persecuted by the Christians.