I typically back up my darcs repositories on different computers. However I do always use the same structure for the different "forests" of darcs repositories. Lately my laptop charger has died which has led me to constantly use a usbstick to move these repositories. Therefore I have started working on a little tool that will automatically sychronise similarly laid out darcs-forests. At the moment it's very bare-to-the-bones. IT will only darcs pull from the repositories in one forest to the other. I later plan to add options to automatically darcs init when necessary (another thing which I've personally missed from time to time).
So, if you find yourself in a similar situation, or you have thoughts, concerns, comments regarding it, feedback is welcome!