Lion Terminal remembers sudo password after quitting
This is normal, and an inherent consequence of the way sudo handles its 5-minute don't-need-to-reauthenticate window.  When you authenticate to sudo, it records your account as having authenticated.  Because the authentication is tied to your account (not a Terminal session or something like that), it's still valid if you quit &amp; reopen Terminal, log out &amp; back in, or even switch to a different session type (e.g. console login vs. SSH session vs. cron job running as your user ID, etc). I'm not certain offhand if it survives a reboot -- if not, it's because there's a step in the system startup process that wipes the timestamp files.

BTW, you can clear your own timestamp file with sudo -K.