What info!? The UDID isn't some magical key that grants developers access to all your data. It's just a number. If developers want user data, they should ask for it. Apple does when you create your AppleID, iTunes account, MobileMe account, or developer account, etc.
Apple HAS to use the UDID for hardware related purposes though, that's the point of a hardware UDID... identifying hardware, not users.
How does it hurt OpenFeint!? I can't believe OpenFeint needs a device ID for users to use the system. I'm guessing there's some sort of login just as with iOS Game Center (I have to log in using my AppleID).