I am addicted to programming for startups. I have learned from 1st hand experience and from CVS logs that on most projects 99% of the check-ins and real coding is done by at most 2 guys (usually 1) on a 8-10 man project. I would say, even though I haven't done a study, I see the hard facts every time I check-in code. There really are programmers out there 20x-30x more productive than the rest.