The iPad is a fantastic, big screen devices with a great web browser and amazing games, and anyone who sees it is likely going to want to borrow it to use or just to try out. If you need to lend your iPad, however, all your personal content, messages, email, etc. get lent out with it. And that cause problems because unlike traditional computers, the iPad doesn't support multiple accounts, or even a restricted "Guest User" mode.
But with iOS 6, you can use the brand new Guided Access mode (or single-app mode) to simulate it.
If you've ever wished your iPad -- or iPhone or iPod touch -- or be locked down into Safari web browsing only, or that you could let someone run a presentation or try a new game without snooping through your personal business, now you can.
If you don't set a Passcode immediately, iOS will have you set one the first time you use Guided Access.
The Home button will automatically be disabled so no one will be able to press it to exit the app you give them and go poking around your device. You can also use your finger to trace a circle around any additional controls you want to disable (for example, you can trace around bookmarks to prevent someone accessing your personal bookmarks).
Bug note: iOS 6 Guide Access on the iPad currently has a bug that causes disabled controls to re-enable when the device is rotated from portrait to landscape or vice versa. However, you can go into Settings and make orientation lock accessible only in the fast app switcher (and not the hardware switch on the side), thereby preventing that bug from occurring. Hopefully Apple fixes this in the next update.
So that's it, with iOS 6 and Guided Access you've now created a faux-"Guest User" mode for your iPad (or iPod touch or iPhone) and can rest easier if someone wants to borrow it, at work, at school, or at Home.