Bookcrossing.com is a great idea in my opinion, but can be a lot of extra work without much payoff. Before you get to deep into it, sign up for alerts of books being released in your area to see if anyone is using it. I live close to Los Angeles and surprisingly few in the area do. I see one or two releases a week within 25 miles, but by far I'm the most active with over 450 releases within the last year. And at that I've only gotten notifications about 4 re-released back into the wild. I've only seen 3 pre-labeled books in a year and a half.