Windows NT (and Windows 2000, Windows XP and Windows Vista) has always had a “guest account”. In theory, you could enable the guest account to allow friends, family members or house guests to access your computer without messing things up too badly. Unfortunately, Microsoft has never made it quite clear (to home users) just what the “guest account” is, and how access rights operate under that user. So most people just don’t bother using it at all.
Windows 7 has a groovy new feature called “guest mode” that’s like the guest account on steroids. It can do this because it uses an improved version of another Microsoft tool – Windows SteadyState – to take a before and after “snapshot” of your PC. As soon as someone logs in under guest mode, a snapshot of your system is taken. The guest user will not be able to change system settings, install any software, or write anyone on the disk outside their own user profile folder. Once the user logs off, any changes made to the profile folder are discarded by SteadyState, and you’re presented with a shiny “new” guest account again. Also, drives can be “locked”, and users would not be able to change anything on a locked drive on your system.
It’s a cool feature, especially for folks like me that are too paranoid to let anyone else use their computers!
Read more about Guest Mode at Lifehacker here.