Not sure how many people have seen this already...
One of my coworkers actually did the biometric security mod on his macbook pro. It's neat, but eh. Not really my cup of tea. Most of us at work make fun of him for it. Since he's also a ACDT/ACPT, he doesn't really have to worry about the warranty issues. It's something of a running joke anymore.
There's a better list of mods here: [URL=http://www.applemacbook.com/mods]MacBook Mods and Hacks[URL]
The mod that iantm was referring to is this macbook pro biometrics mod.
Word on the street is Apple plans to integrate biometrics for the next generation of MacBook Pro laptops.