Adeona: A Free, Open Source System for Helping Track and Recover Lost and Stolen Laptops
adeona.cs.washington.edu
adeona.cs.washington.edu
There are certainly some testimonials for the paid services but most of the problems solved are recovering lost data rather than the laptop itself. It makes me think that decent encryption and regular backups might be just as good.
I hope to never be able to say I've really used it...