I've thought about that in the past too. It seems convenient to have everything in one place, like in the SVN, with set relative references to dependent APIs. It also seems like a lot of separate repos to host, and I'm not aware of any repo organization options on GitHub.
With that said though, the more I use Git, the more I think things should be split into separate repos. It's just a mindset that comes from using Git. As for keeping things in one place, it's entirely possible to create a master Git repo, which includes all the other repos as sub-modules. That could allow for one solution which contains all the various level projects, while still allowing them to be their own projects in their own right.
At any rate, I don't currently want to move existing projects, so much as start new projects using GitHub. One of the reasons is simply momentum. Trying to sort out the differences, and move things over, before we are familiar with the new system seems like a lot of work. Work I don't feel particularly inclined to do. I figure try out the new system on a few new projects, see if you like it (I've been liking it), and as it gains momentum, there will be a natural push to bring the other stuff along as it's needed.
As for learning Git, I was thinking a pair programming session could go a long way towards building that familiarity.