I'm not entirely sure that there isn't one already or if it is possible. I searched the market and this forum and haven't found anything.
I think it would be nice to have an app that disables all personal information. When you have a phone that uses android, you are bound to get the "Hey, can I play with your phone?" It would be nice to press a widget and have it log you out of facebook/gmail/twitter/etc. and make it so they can't mess up your settings. Once you get the phone back, you press the widget and sign back in.
I've only had the phone for 3 days, so it's likely that I am already passing over an option in settings.