I've joined in with the postcrossing project, which seems to be gaining popularity with a lot of young people across the world. The project is very simple - sign up, get an address from the system, send a postcard. Once the other person receives the card they can post a picture of it on the postcrossing site so that other people can see it. And of course, you get postcards from all over the world as well.
This doesn't really have a lot to do with writing a suppose, but I find thinking about other places helps inspire all sorts of settings for stories, and reading letters from other people does give insights that can help flesh out characters.
And it's fun!