LoJack comprises software and a service, and will track and reclaim your laptop in the event of theft of loss. The software sits in your PC's BIOS, so short of bricking the blessed thing there's no way a thief can get rid of it. LoJack for Laptops works for both Macs and PCs.
Ludicrously popular in the States (where 'LoJack' enjoys similar brand ubiquity to 'Hoover' or 'Biro'), LoJack is not cheap. At £45 a year, getting insurance may be more cost effective for protecting your hardware.
But Absolute Software told PC Advisor that it has an 85 percent reclaim success rate in the UK (small country, fewer places to hide), so for those people who regularly carry sensitive and valuable data, it may be an (ahem) Absolute boon.