Edit - duplicate (didn't realize posts were moderated).
BTW, there is some risk in this, it's possible for the fs to be really messed up and require manual fixing but I only know of a couple 'nix SysAdmins even capable of it (I am not one of them).
Backups are your friend! After I get an RPi sd card how I want it, I'll use one of the image reader/writer programs to make an ISO/IMG file of it. I usually use Win32 Disk Imager.