Developers TheZimm and Evil Penguin – they also developed Vibe Lock and iNoRotate – released iAccounts today, and app that you can use to create different accounts on your iPhone and iTouch just like you would on Mac or Windows.
This will allow you to lock certain apps , as well as lock other things such as icon moving, search, and even WiFi. You can set options by user, rename the current user and show the user name as your carrier.
iAccounts is available in Cydia store via BigBoss repo for $1.99