This is an old trick that I'm sure has been highlighted elsewhere at length, but to me felt like a new discovery. There's a place on your computer where the machine automatically saves things you've been doing. It works like a browser history and is helpful if you just can't find what you were working on yesterday.
On Win7, you can find this here:
C:\Users\USERNAME\AppData\Roaming\Microsoft\Windows\Recent\
If I remember correctly, this had a standard presence on your start menu back on Win2k and before, but somehow got pushed out, and I had a hard time finding it. Right now I'm working day to day on any one of a hundred different files on my machine so this has become increasingly important.
Note that unlike browser history, if you want additional privacy, just clearing this folder is not the answer. Definitely look into disk encryption and programs like CCleaner and BleachBit.