Ask HN: Tame a mess -- backup & revisions across several systems?

I am a freelance mobile developer, and have many projects spread out over 4 systems - 2 Win7, Mac OSX and Ubuntu. Some of the projects need to be checked into client source control.

What is a good way I can backup, keep personal revisions and share across all 4 systems? The thing that makes it tricky is some clients have their own git or subversion repositories.

Here are my thoughts:

On my main system, have two mostly mirror directory trees: one just containing source pulled from client repositories, and another that is my "working" source tree which contains everything including copies of client files (but excludes their source control system files.) The working tree would be checked into a local git repository.

So for the various tasks I need to do:

Update from client repositories:

After updating from client repositories into the client tree, I would merge all source files (no svn or git files) to the complimentary location in the working tree, then checkin any changes to my local git repository.

Committing to client repositories:

Merge source from the working tree (no svn or git files) to the client tree, then commit.

Sharing between other system:

The other systems would just update and commit to git on my main system.

Backups:

Backup the git repository, the client "tree" and the "working" tree to an external drive.

Any problems with this? Is there a better way to do it?

Thanks