These are a couple postcards I've recently received. The one on the left comes from Puerto Rico and the right, obviously, from North Carolina. The U.S. is a big contributor to the program, perhaps by dint of its tremendous population, but frequently I receive addresses to/from Finland and Germany as well.
I'm grateful for the program: I love the access to international postcards as well as the stamps they come with--usually I scan these in and add them to my online collection. I've historically had pretty bad luck with regular pen pals around the world, so this at least satiates my need to talk with new people. I try to send out interesting postcards when it's my turn to issue them. Perhaps the most difficult thing for anyone to do is think of interesting blurbs to write on the back. One guy in Croatia thought he would relate everything the average Croat knew about Minnesota, which was comically little. (It would have been even less if I wrote how much Minnesotans know about Croatia.) I responded with two postcards depicting a map of the state and a list of trivia.