Beware sleeping your Mac from a FileVault account! I have a FileVault-enabled non-admin on my PowerBook G4, and I have it set to require a password to wake the computer from sleep or screensaver.
If I close or sleep my PB under this account (or choose Lock Screen from the Keychain menu), then wake it, the system asks for password authentication. However, if I then type the name and password of an admin account (instead of the FileVault account), voila! I get full access to the encrypted account and all FileVault contents.
The screensaver authentication is apparently significantly different (and less secure) than the loginwindow authentication.
[robg adds: I haven't tested this one, so if someone who uses FileVault could confirm it, please post your results in the comments.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060705184726593