The issue that puts me off installing something like this (or even just a cron script that pings my webserver) is the problem needing to allow the thief to log in enough to connect to the internet. I'd rather have screen lock after suspend, and password log in.
so in order to do this securely it really ought to run during GDM. but for that to work it would need to automatically connect to networks. or to have a guest login.