Vavle Stats on Achievements

I happened on this page today:

http://www.steampowered.com/status/l4d/

Gives the overall percentage of players that have the various achievements. Surprisingly, Lamb 2 Slaughter is the rarest (As an infected, incap a survivor who has entered and left a safe room). I would have though 'Nothing Special' or 'What Are You Trying To Prove' would have been the toughest.

8 more to go for me.