iPrivacy is a Cydia tweak that I think should definitely become a native feature of iOS in the future but basically it allows users to set up a "guest" account for use of your phone just like you can on a personal computer. This way you an allow someone other than yourself to use your phone without gaining access to sensitive information photos, and other personal effects. The way it works is simple: you have two lock codes. One for the guest mode and one for personal use.

Cydia Name - iPrivacy
Repo - BigBoss

nice post dude, thank you. another good privacy app is 'applockr' lets you set a pass-code on any app/folder

Or you can use sbsettings and hide any app completely from your springboard