Two very intersting post-mortems about the trouble with git.kde.org from last weekend and what you could learn about backing up Git repositories.

Distillation - Me, my blog, and my Johnson by Jeff Mitchell on Jefferai

How KDE's 1500-repository Git system was nearly destroyed, and how we're preventing it from happening again.

Distillation - Me, my blog, and my Johnson by Jeff Mitchell on Jefferai

Backing up huge numbers of Git repositories isn't as simple as you might think. Here's why.

This is a really nice solution that I was looking for. I use this to make configuration file changes on my staging system without the need to ignore the whole config file.

Add your config file in .git/info/exclude and then use git's update-index:
$ git update-index --assume-unchanged path/to/file 

For a better explanation take a look at this blog article:
Ignoring local changes with Git on Stuf

If you have configuration files or any other files in the local repository that you would like to keep as they are without the danger of adding them by mistake in a commit, you can specify that using the local git exclude file and update-index....