When enabling whole disk encryption, be sure to save the recovery key externally from your laptop.  I recently upgraded to Mac OSX 10.7 (aka "Lion") and enabled the new whole disk encryption feature which is now part of FileVault.  Before encryption begins it provides the recovery key but it's up to you to save it offline (no USB flash drive option).  Thankfully I did this because when I rebooted it prompted me for local admin credentials which of course I changed and didn't remember.  Without the recovery key saved on my home network I would have been in big trouble.