Well, it would be interesting to know if anyone else has any insights as to team-size.   2-3 people seems most typical; teams of 4-5 are usually on two projects at once. And as long as they know how to manage, or are, more likely, under the purview of a project manager who knows how to give them a little distance (but, not too much), it seems to work okay.   But I have definitely found (as Mechanism openly states) that “a project manager who knows everything about project management but nothing about software ... can’t manage a software project.”

Single-person projects, or teams or departments that are led by an autocrat who styles himself “head geek,” invariably are a certain recipe for disaster.   (Especially the latter.)   I think it’s really important that the key people on the team have knowledge of facilitation ... and diplomacy ... as well as above-average technical “chops.”