On that particular swap site, when I post a book, it automatically notifies me that the book is wishlisted. It's not a guarantee that it will get requested right away or at all, but it's much better than the other site I belong to which doesn't purge inactive accounts, so something could be wishlisted by 20 people who haven't been to the site in five years. When I got home from mailing the first book yesterday and marked it mailed, I saw that I had another request, so I'm off to mail another book today. :)