Richard Jones' Log: Language metrics from ohloh
ohloh tracks open-source projects and amongst other things has a neat set of tools that allow you to compare languages, projects, etc.
You can look at the relative number of commits to projects for Python, Perl, Ruby and PHP with C/C++ and Java or just just Python, Perl, Ruby and PHP. Python's doing pretty well with a popularity about the same as PHP. Also quite interesting are the plots of contributors and active projects (Java and C/C++ in decline). Then there's the huge dive in C/C++ commits in the last 6 months as seen in the plot of the number of commits per language.
Interestingly C# (about the same popularity as Perl or Ruby) hasn't made nearly the same splash in open-source as Java did.
Via the Python language statistics page you can also find out that Fred Drake is apparently the most experienced contributor of Python code. I'm not sure how they calculate that one since I'm listed as the 7th most experienced Python contributor but there's got to be others with more - Guido for example ;). The Recently Active Contributors list is also interesting to find out about active Python-based projects.