There are plenty of ways to secure the data on your laptop. There’s FileVault, which encrypts your entire home folder and often causes corruption-induced heartbreak; you can store your files in the cloud using your iDisk, a home server in conjunction with Back to My Mac and MobileMe; or Google Docs, where you can keep your laptop free of any sensitive materials, keeping them instead on a flash drive.
You can use a firmware password to set up low-level password protection on your Mac. If it were stolen, the thief would have to know the password in order to use the computer at all. Of course, he could extract the hard drive and access your data, but the computer itself would be useless.
Setting a firmware password on your Intel Mac blocks the use of T, N, or C to put the computer into Target Disk Mode, NetBoot mode, or boot from optical media. It also blocks the ability to start up in single user mode, verbose mode, to reset the PRAM or boot disk in boot manager. Of course, you are required to enter the password to boot up normally.
If you forget your firmware password, there are ways for your authorized service provider to get around the security. Be prepared with some undeniable proof of ownership before you ask to have the protection removed. And no, I cannot disclose how to circumvent the password!
You can read more about this hidden feature of your Mac at the Apple Knowledge Base: http://support.apple.com/kb/HT1352?locale=en_US