What about an opportunist though? Someone you know could snatch your keys from the table at a bar, but snapping a picture of your house keys leaves you unaware that anything has happened, until they rob your house.
Of course you'd have to be hanging around with some pretty shady people for this to happen, but you don't always know everyone at the table well...
EDIT: That said, I really like the idea. I wish something like this was available in Europe.
Right now the computer vision isn't really well optimised it takes about a minute to go through the process. Give me a wad of blu-tack and I can get an impression of your key in a couple of seconds.
Valid point though, I've thought most of the security concerns through from a logical angle and I'm pretty happy with the situation, but potential customers will just make a snap judgement based on 'feel' .
Of course you'd have to be hanging around with some pretty shady people for this to happen, but you don't always know everyone at the table well...
EDIT: That said, I really like the idea. I wish something like this was available in Europe.