A friend has just told me about Ohloh, a web site that analyzes the activity of open source projects by scanning their source repositories. It is quite nice! It generates statistics about the recent activity of each registered project, the languages they uses, the people working on them... And, for each developer, it accumulates statistics about their work on the different projects he has contributed to, automatically building a developer profile.
You can add your own projects to the site, which is a very easy procedure, and create an account to have your own profile, which is useful to merge all your contributions to various projects into a single person. I.e. if you have contributed to one of the registered projects and search for yourself, the web will return some hits; if you have an account, you can claim that you are that person and link your contributions to multiple projects into a single page.