On another note, you know what else could be a great source(s) for data? Google Scholar, CiteSeerX and arXiv. It'd be really interesting to compare the language usage between "industry" and academia.

I think StackOverflow has; GitHub still seems a bit biased towards scripting languages like Ruby or Javascript though. In any case, since you show the graphs from the various sources, I don't think it matters if one source is more biased than another. If, for example, you used CodePlex as a data source, you'll see a huge bias towards C# -- but visitors to your site could simply draw their own conclusions from the charts.

If nearly all ruby programmers put their code on github, and you don't count it but you do count google code, then isn't that a bias i the sample? Wouldn't it make more sense to include all the major code hosting sites, including github?

This is, by the way, an honest question. I think at a certain point they'll be mainstream enough to say yes, but it's tough to say when.