One of the security options that’s good (and fairly painless) to enable on OS X is secure virtual memory (AKA encrypted swap space.) On 10.4 and 10.5, you can enable this from the Security preference pane. On 10.4, you could also enable it from the command line by adding an entry for ENCRYPTSWAP=-YES- to /etc/hostconfig, but this has changed in 10.5. It took me a while, but I found an defaults write command that turns on secure virtual memory:
sudo defaults write /Library/Preferences/com.apple.virtualMemory UseEncryptedSwap -bool YES
You will need to reboot before the encrypted swap takes effect.