If you’ve installed Mac OS X 10.7.2 and rebooted or ended up…
If you’ve installed Mac OS X 10.7.2 and rebooted or ended up at the lock screen, you may have noticed that a new “Guest User” account appears at the login screen.
This is not a full guest user account, if you select the Guest User option at login, the Mac will restart to a secured Safari-only version of the OS with access to the internet. So what’s the point of this? It turns out this is part of setting up iCloud in Mac OS X, specifically the “Find My Mac” feature. The Safari Guest User allows someone to get online so the Mac can be located, but prevents the Safari user from accessing your files and applications.
I’m going to highly recommend keeping the Guest User Safari account enabled so that if you happen to lose your Mac, or if it’s stolen, it could easily be tracked down. Nonetheless, here’s how to turn this off if you don’t need it for some reason.