Hmm
Other ideas - top up in the off-licence or corner shop to avoid CCTV, buy a card every time you come to London and use it *once* (National Express sell them on the damn bus), touch in but don't touch out (costs four quid a time but they won't know where on earth you left the Tube), fry the card during the journey then social engineer your way past the barriers...
No, I've no idea why they'd want to use a system that's already easily defeated as an efficient people tracking mechanism. The most useful thing you can data-mine out of it is how people move around London in order to improve public transport in the right places, which I'm certain TfL do already, and which is a perfectly sound use of the data.
