I use the free version of Prey and I think its great. Installed it 8 months ago and forgot about it. Glad to have some sort of safeguard just in case the worst happens.
I use Prey and even took a test run with it. Worked great. Just make sure that the recovery data is sent either to web mail or that you don't save your mail password to the keychain. Wouldn't want to let the bad guy to know it's there if he gets nosy and looks at your mail!