I also 'lost' my CD key when I came back home from the States earlier this month. I didn't have enough space/weight allowance to take all the cases/boxes of the games I bought with me; so I ditched them at the last minute. It was only when I was already back home in Mexico and installing the game on my gaming computer did I remember that the CD key was on the back of the case and not on the manual...

Quick call to my brother got it sorted out; if I had waited a day more, it would have been thrown out and really lost... so I feel your pain.