An unadvertised feature has been found in the latest Lion Developer build, says MacRumors. It enables a Mac to be used as an internet kiosk and nothing else. The "Restart to Safari" can be found on the user lock screen and allows unauthorized users to use the Mac only to browse the Web. When in "Restart to Safari" mode, the only window that will appear is a Safari window.
There are several benefits to the "Restart to Safari" feature. First, it will allow unauthorized users (those without logins) of the Mac the use the computer as a web kiosk. This is a handy feature when a member of the same family, for instance, wants to quickly look up something on your work computer in the den. There's no logging in or creating a separate user account. The Safari browser that they see will not show any of the bookmarks on the Mac either.
Another use for "Restart to Safari" is to allow the Mac to access the internet so that Find My Mac can locate the computer if it's missing. If the laptop is stolen, the thief won't be able to access your personal files, but may continue to use the Mac in "Restart to Safari" mode, thus enabling time for Find My Mac to locate the missing computer.
Apple OS X Yosemite