I am a Prey user and i can share some of my knowledge with you.
On laptop indeed, formatting and reinstalling the OS means prey is gone.
However, you can prevent this from happening.
On the laptop, if you password protect your BIOS (for CMOS Setup, not for boot) and force it to boot only from Hard Drive, it can protect from hard disk format.
Also, what I did is to setup a limited restricted user (with access only to few things, with no account password), and an admin account with password. This way:
1) Thief cannot reinstall OS (BIOS password)
2) Thief cannot use HirenBoot / Windows DVD or any other bootable CD to format drive or reset Windows password (because of Hard Disk first force boot)
2) Thief is forced to logon into the limited account I set up since he doesn't know the Windows Password.
Basically on this limited account I have set up policies that block EVERYTHING except the internet browser. So he cannot access any of my data, cannot plug in any USB devices or DVDs, cannot uninstall programs or delete files or view any of my sensitive files... basically cannot do anything but access the web browser.
And while he/she is doing that I am silently collecting info in the background... sites he visits (Maybe he visits Facebook or twitter or shopping websites...) . I get his Location, his Identity, all the info I need, without him/her being able to do anything.
So i give the thief access to enough resources to encourage him/her to use my pc (so I can track it), and restrict enough info so he/she doesn't access anything on my computer and cannot change settings.
Is this method foolproof? probably not. Is it very difficult to bypass? Most certainly yes!