This is why I love Bookcrossing!
As I have told I really like the idea of Bookcrossing. And the practise too! One of the best Bookcrossing-experiences I have had was with Neil Gaiman's "The Sandman, A Game of You"-graphic novel. Somebody had left it to a cafe here in Oslo and I took it with me. When I had registered to Bookcrossing-page that I had found the book I one day got email from India(!) from a young woman who was also a bookcrosser. Her boyfriend was going to be 25 years old and because of this she wanted to give him 25 books for present. So this nice girl from India asked if I wound like to send my Sandman-book to her when I had read it. And well, that's exactly the idea of Bookcrossing, so of course I wanted to do it! So I read this book (and liked it a lot!) and after that I sent it to India to this woman who gave it to her boyfriend who obviously had a very nice birthday (who wouldn't with 25 new books?) and he also liked this graphic novel and so everybody lived happily ever after.
Don't you just have to love Bookcrossing?
Here in Oslo we actually have couple of cafes where you can find a Bookcrossing-bookshelf, where whoever can leave their books or take them with them. It is safer to leave books there :-) And many bookcrossers have meetings too, where they can change books. I have been in one meeting and it was really nice, but after that I haven't had time to go to meetings.
I do understand your worries but in a way I also love the idea that the whole world is a one big library and you can find books wherever.
Some bookcrossers also go "hunting" books when they see that someone has released books aroud their neighbourghood.
But of course quite often you don't hear anything from your books afterwards. Then you can just hope that it is making someone else happy somewhere :-)