Adding my 2c...
For the ocPortal project, we switched over from running our own svn server to github. I was very skeptical at first. Having to do separate commits and pushes seemed like a pain. The extra complexity seemed like a pain. It annoyed me that both git, Mercurial and Bazaar all do the same thing yet git it a bit harder. But actually it's really fantastic for these reasons...
1) Github provide a really high quality UI for browsing commits and code.
2) Github take away from the need to maintain you're own infrastructure, and it's free for OSS projects.
3) Git is insanely fast.
4) Git handles merging and branches much better.
5) Pull requests.
And git is winning, so at the end of the day you have to pick the right horse.
I totally understand the desire to stick with what you know, and to not have to reinvest by throwing out what you already have. Running a project that goes back 9 years myself, I know it's annoying to keep changing everything if it's "not broke" for what just seems like a fashion trend. However a whole generation of people are growing up around git and groups that don't adapt *look* like dinosaurs when viewed through the perspective of someone used to better tools.
I'd also suggest not to get stuck in paranoid mode about wanting to control everything yourself. There are so many advantages to relying on github, and it's very reliable. Even if it did all go to crap, you could just switch to your own git server or whatever.
I can't recommend changing enough. And full respect to you guys ISPConfig is awesome. I don't mean any rudeness at all, I wanted to share my own experience.