I've never used a source code management system for any personal projects. However, I just started using subversion after (1) hearing a lot of good stuff about it at OSCON2005 and (2) reading the first few chapters of Pragmatic Programmer, The: From Journeyman to Master, which strongly encourages using a SCMS for every single line of code you write.
I've immediately found reassurance in having my project in subversion. I don't have to worry that a change I make might be hard to reverse. I can always revert to a previous revision. I'd definitely recommend using a SCMS for all your code. I'm still trying to figure out how to organize all my code to be kept in subversion, including any "throw away" scripts.
By the way, I'd highly encourage anyone who does any coding or application design to read Pragmatic Programmer, The: From Journeyman to Master. I'm about halfway through, and it's quite good. It feels like the sort of book that you'd want to keep around and occasionally go back to, just to refresh your mind and get a new perspective on whatever project you're working on.