One of the Classpath developers pointed me to their CVS statistics when I asked them how actively their project is currently developed, i.e. the number of active developers.
The pages are generated with StatCVS, so I ran it one the CDK too:
I knew I did a lot of work on the CDK, but never realized that 62.7% of the commits were mine! Keep in mind, though, that a lot of these commits are for code maintainance! Next in line are steinbeck and rajarshi. In total 28 people commited patches to CVS, though other people contributed patches too, which were commited by a developer with write access. There is jump in the commit messages somewhere this summer, which I think is the move of the data directory from cdk/data to cdk/src/data.
The full analysis results can be found here. It was generated with the StatCVS version in sid, and will rerun it soon with a more recent StatCVS version.