[LogicX]

Yes, the new filevault does make things tricky in this sense... however its just a matter of time til someone improves prey project to install to the new OSX Lion un-encrypted install (the one your system boots to, and prompts you to enter your credentials, before booting into the encrypted drive).

There's apparently a safari browser-only mode which can be activated from the login screen there.

This would create the ideal scenario for the stolen laptop: Thief without the knowledge or ability to reformat (particularly if you've slowed them down further with a firmware password) can only use the safari-browsing guest mode; can't get to your full encrypted drive, and Prey is recording and sending off everything they're doing.