Consider this your daily reminder to BACK UP YOUR WORK.
Jumpdrive. E-mail. External server/harddrive. DO IT.
Once a week is NOT enough. You need to back up your work EVERY TIME YOU WRITE.
There is no way to know for sure that your computer won't crash tomorrow. That your harddrive won't burn out. That a virus won't wipe everything clean.
I e-mail my files to myself after each writing session. I keep using the same message over and over again, so everything is neatly together and in proper chronological order. What is your favorite/suggested method?