at the beginning of the year I attended a few interviews at various places and were clearly unsuccessful as I never heard back from them at all, and I was quite angry. It would have been polite and helpful if they had just called me to say thank you for spending the time and money to attend the interview, unfortunately you weren't successful as we feel such and such, but thank you for coming to see us, wish you luck in your search.
I think its just polite of someone to do that as for one interview I had to pay £20 to get there and back and I never heard anything from them again.