I care more about the safety of my data than the safety of my computer, so I have FileVault full-drive encryption turned on. I don't think a thief could log into my computer without wiping the drive, which would wipe Prey if I had it installed. So I'm not going to bother installing it.
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.
