Found out something interesting today: if you wave your Oyster card in
front of the reader on a touchscreen ticket machine, it'll give you
the option to look at a list of times when you've used the card, the
cost of each use (0.00 in each case at the moment as it's only
Travelcards) and the location it was used (which counterintuitively
only shows bus numbers and not tube stations at the moment).

Well, it amused me, but that's easily done.