I think the biggest problem here is one not even mentioned: What happens when the information is wrong? Passengers swapping seats isn't all that uncommon -- I've done it many times to allow families to sit together -- but the computers aren't going to know that has happened.

On a recent flight I swapped seats with my girlfriend -- she wanted the window -- and the service director was clearly flummoxed by the fact that the man in front of her was "Elena" and the woman sitting next to me was "Colin". (I'm guessing that they've been told that they should never assume genders based on names, but she could clearly tell something was off.) In that particular case, the confusion was quickly remedied; but I can only imagine the embarrassment which would ensue if flight attendants start singing happy birthday to the wrong passenger.