I used Find My Mac, but for some reason the code didn't lock my mac until iCloud beta 4 and Lion GM. I didn't know what it was. I entered tons of passcodes that I thought I would have made it, but none worked. I feel like I entered the right password, but just like the person below (see quote), It won't accept it. Additionally, I had a firmware password on it. The problem is because of the firmware password I COULDN'T boot from a DVD, reset the PRAM/NVRAM, or anything else. The two locks worked together from preventing me from booting any source except the locked drive. Even when I correctly entered the firmware password and selected my boot medium, it would revert back to the locked screen. I took it to the Genius Bar (even though Find My Mac hasn't "officially" been released). After waiting for an hour and a half, they pulled out the hard drive, formatted it, reinstalled lion, tried to reset the Firmware password by changing the RAM. Nothing worked. Now, they're replacing the entire logic board. Good thing it's under warranty, because it's $530 to replace. This will take nearly a week. The said Apple Engineering will look at the issue, but hopefully in the future firmware passwords and Find My Mac won't permanently lock Macs. Just make sure you don't establish a firmware password. Then you can always reset the PRAM/NVRAM if you get locked out.