I made something kind of similar that also estimates how much time it would take to finish your backlog, and guesses what games you have and haven't beaten:
Nice work. My original idea was to have it randomly generate a calendar which would designate games to certain days in an attempt to force myself to play some of my unplayed games (currently 138/269 games), but this was just a fun little thing I did when drunk and got bored of the idea. :D
http://steamplaytime.appspot.com