It sounds like the latest developer preview for Mac OS X Lion will allow you to reboot into a Safari only mode (similar to how a Google ChromeBook is perpetually in Chrome-only mode), as part of the upcoming Find my Mac feature. Should iPad have that option? iPhone and iPod touch?
It would be handy if you wanted to give someone easy access to the web but didn't want them nosing around in your pictures, iMessages, email, and other personal information. It might also be good for educational, business, or even kiosk settings where web access is enough and apps might be too much.