Being the nerd that I am, I use source control to do something like that.

A neat feature of Blender is that in the save dialog you can press + or - to automatically add or alter a numeric extension at the end of the filename, so it's easy to keep version'd backups. I miss that in a lot of other software. Of course, I also find myself pressing "X" to delete things from time to time, or starting a lot of words with an 'i'. I don't think my brain is set up to handle different things very well.

Back on topic I've been bitten once by the ol' "save and suddenly the document doesn't open" trick. So I make sure to always occasinally save a copy in a separate file as emergency backups along the way (besides using source control for revisioning) just in case.