If you really want your data with you at all times, then a subcutaneous PDA will be the only way to go. A humorous version of this is the ass chip that seems to pop up all over E2 these days. Really, though, a modification of the MIT Media Lab's shoe computer, that stores contact info and trades it with others through electrical transmission via handshake, would be a useful tool. Simply shake hands and nab contact info for later. Very handy for those who have to attend lots of trade shows. This wouldn't really require any technology that we don't have today, either; if it had Bluetooth, synchronizing it with your desktop system would be easy! There's no real limits on where it should be implanted, either, given that it speaks with electric current and radio...you could put it somewhere easily accessible and non-critical like the forearm or tricep area, making it easily removable in case of problems or upgrade.