It there's one thing really irritating about leaving your iPhone out with friends, it's when they unlock to unleash all kinds of madness (usually on your Facebook) while your back's turned. You can always use a passcode, but maybe it's time to add an extra step to the "Slide to Unlock" screen, by adding facial recognition.
RecognizeMe is an app aimed at jailbroken iPhones, and basically gives you the option of not just using a passcode to unlock your phone, but to require facial recognition too. After adding a few images into an image gallery ("Training Sets"), the app will simply give you the option when you next try to unlock your phone to either type in a passcode or use facial recognition.
It'll scan a few times before deciding if you are the real owner of the phone--though you can adjust the security, meaning people who look ever so slightly like you might be able to get in.
Although the creator (currently only found on YouTube) says it's still a little rough, a few testers have found that even pushing the security to "80% secure" still lets others in, and that it can take up to 20 seconds to verify you. Still, if the sheer sight out the app scanning their face is enough to keep your friends from leaving strange status updates on your social networking profiles, it's worth it.
Although it's not quite available to the public, it is currently processing in the CydiaStore and it's believed that it'll cost $6.99 when it becomes available. Check out the video to find out how it works.