It's also a good idea to not carry around something as important as the USB drive you backup with around on a keychain. I leave my USB drive at home in a desk drawer, and if I have to take it with me, I put it in a zippered pocket in my laptop bag or back pack.
At least you didn't lose anything, and you're just backing it up now.
I have been saving all of my notes and outlines on a USBS stick that I carry around with me on my keychain so that I can work on things at my PC and on my laptop. I went to Houston this weekend and when I got back I realized that my USBS stick was no longer on my keychain.
I have been intermittently backing up my disk but even so I have lost about 2 weeks of notes and outlines in two of my classs.
Don't make my mistake! Back up your notes every couple of days.