I use (free) cloud storage service for this. Dropbox is my favorite. When I create a new project, instead of have it saved to the default location (my documents > visual studio xxxx > projects folder), I select the dropbox folder. Everything then will be synced automatically to dropbox, which I can access from other computers too.
It doesn't directly answer your question about automatic backup, but it actually does more than that. Dropbox automatically saves different versions of files that you can use to revert unwanted changes.
Give it a try and you'll probably like it.
Let us have faith that right makes might, and in that faith, let us, to the end, dare to do our duty as we understand it. - Abraham Lincoln -