I have mentioned this site several times here on LJ, so have many others I noticed. But I have to state again how much I enjoy the concept. Some of the bookcommunities here do a good job in telling about books, recommending new authors etc. But none of them go as far as BookCrossing. In the past years I have released over 50 books. Nearly 40 of them in the wild. Which means I have left books in trains, at airports and gasstations, on benches in towncentres and on other places I think someone might find them. The fun thing is that you don´t know what´ll happen with the books. Sometimes you see someone pick up the book (train!), sometimes you know it has been found, as it isn´t there anymore sometime later. The best way to find someone found it, is that the finder has registered the book on the site again. Unfortunately this does not happen too often, but knowing that someone has found your book, regardless if he goes back to the site or not is good enough for me.
Next to these wild releases, I have swapped several books with other BookCrossers from several countries. Also I am participating in some bookrings, a book that travels passed several readers before returning to its owner.
Several forums are very active, talking about books, bookrings, television programmes on books, swaps, meetings, markets and anything you can imagine.
Another nice thing about BookCrossing are Random Acts of BookCrossing Kindness (RABCK), which basically means you send a book to someone as a gift. I have sent out some books and have also received one book just like that. Book readers are nice people. If everyone would read more, the world would be a much nicer place.