I have my Blockland key stored on the e-mail I purchased it with, and then written down on a piece of paper.
The same is true with essentially all of my activation/serial codes for games and products.
Why would I need to bother with silly encryptions or wasting time memorising long lists of numbers?
I'm not entirely likely to lose the written info.
If I do, it'd either be due to it being stolen (in which case, some robber now has my Sims 2 activation key?), or if I lost it in a fire or something.
In which case I'd get it resent to the e-mail, and really, it'd probably be the least of my worries after a disaster like that.
The Blockland Forums is the only place where I've met so many people so seemingly paranoid about storing their activation codes.
That or you all insist on knowing it incase you have to re-enter it. How often does that occur, really?