This Computer Weekly piece pointed me at a project that's studying immigration into open source projects. Interesting stuff: the curves are similar to the naked eye, so my next two questions would be:
See also Susan Sim's paper on software immigrants: these concerns aren't traditionally part of software engineering, but I believe they have as much influence on success or failure as technology choices or modeling tools (probably more).
- What factors account for the differences between projects?
- What do the curves look like when you divide the population by first language, geographic location, gender, age, etc.?