Are there any popularity / usage statistics available for the Free RCS/SCM/VCS systems?

Question

Are there any surveys anywhere which report on number of projects and/or people using the assorted Free version control systems?

Also interesting is if a similar survey was one over time, to see how things have changed.

Obviously, it's hard to measure this sort of thing completely accurately, but it should still be possible to get reasonable estimates.

Since tags are annoyingly limited to five items, and I didn't want a bias towards/against any of the systems, for search purposes I'll add the following: bazaar bzr cvs git hg mercurial rcs scm svn subversion vcs scm vcs popularity survey statistics
update: Very few views so far, so I'm cycling the tags to contain the main tags for each software, which might get more eyes on it. If only I could just put all the tags together!

Answer 1

Git User's Surveys (2006, 2007 and 2008) did contain version about other SCMs... but this is of course biased. You can check how many people have given SCM in stack at Ohloh, open source software metric site, but I think you can check only current state. There are also results of Debian Popularity Contest (popcon); you can even find some popcon graphs somewhere; here I am not sure whether one can get historical information.

Neither of those sources is a good solution, but I think it is a start...

Added 20-05-2009:
There is also GNOME DVCS Survey results analysis (with links to raw data) on Elijah Newren’s blog (DVCS = Distributed Version Control System).

Added 28-05-2009:
There is Survey on Decentralized Version Control Systems by Brian de Alwis of Department of Computer Science in the University of Saskatchewan being run (see this announcement on Mercurial and Git mailing lists).