For the "bear essential" in Mac OS system consistency and security

An interesting discussion on our mailing list turned up this product, Faronics DeepFreeze Mac, which
Once Deep Freeze Mac is installed on a workstation, any changes made to the computer—regardless of whether they are accidental or malicious—are never permanent.[...] Deep Freeze Mac ensures computers are absolutely bulletproof, even when users have full access to system software and settings. Users get to enjoy a pristine and unrestricted computing experience, while IT personnel are freed from tedious helpdesk requests.
Looks like it's aimed at Educational, Corporate, Governmental, Hospitality, and Library environments. And looks like there are flavors for Windows, Windows 2000/2003 servers, and Linux as well. Thanks to our local Apple rep, John-Erik, for the great tip.