> Fred Brooks concludes that no software product should be designed by more than two people.

That really depends on the architecture of the software. There are thousands of people creating and maintaining device drivers for the linux kernel. The idea that only two people could do that simultaneously, is a bit far fetched when the architecture actually makes sense.

But then again, most commercial software does not have that kind of extensible architecture. Therefore, it is probably true that a commercial software team will never really scale.