During WFP07 it looked something like this on the backend:
45% Ruby (mostly RoR, but one might not have been using Rails)
30% PHP
15% Java
10% Perl
Almost all of the groups were heavily using JavaScript, as well. In fact, some of them were predominantly JavaScript with quite lightweight back-ends (Zenter and Weebly come to mind). Heysan were predominantly Flash at the time, but I believe they have a lot more PHP back-end code now.
45% Ruby (mostly RoR, but one might not have been using Rails) 30% PHP 15% Java 10% Perl
Almost all of the groups were heavily using JavaScript, as well. In fact, some of them were predominantly JavaScript with quite lightweight back-ends (Zenter and Weebly come to mind). Heysan were predominantly Flash at the time, but I believe they have a lot more PHP back-end code now.
I don't believe there were any Python projects.