No one wants other people messing around with their computer when they're away from their desks, but what can you do? It's not practical to log out every time you want to go for a cup of coffee, so many people put a password lock on their screensaver instead.
This is much more convenient, but it has a serious Achilles' heel: if you are in an environment where many people have logins on your computer, such as an office with centralized login (NIS, ActiveDirectory/Kerberos, LDAP, OpenDirectory, NetInfo, etc) where everyone has an account on every computer, then anyone can use their own login to disable your locked session. The only record of this will be an entry in
For a lot of people, this probably defeats the purpose of locking the screen to begin with; until & unless Apple provides a way to change this behavior, it may be wise to avoid the screen saver lock and fully log out of the system whenever you will be away from your computer for a long time (lunch break, overnight, etc).
This may only work for Admin users, which would be a lot less serious than I was thinking at first. I need to test that...