I had stuck one on a vending machine at a rest stop and one of the attendants found it and contacted me with a very encouraging message on Facebook. :) I am also pretty sure the one at the Half Price Books in Fort Worth was picked up as I placed it, went to look around the store and when I came back by on my way out it was gone.
I am glad I did this with postcards this year. I would have been a little wary about leavin' an original piece taped where someone might just toss it in the trash (not everyone appreciates art if you can believe that). I also liked placing so many out there for people to find. It gives more people a chance and I had fun finding places to put the postcards and photograph them so people could find them if they went lookin'.