"We all know books burn -- yet we have the greater knowledge that books cannot be killed by fire. People die, but books never die. No man and no force can abolish memory... In this war, we know books are weapons."
BookCrossing.com isn't free to keep running, and as it grows, it will require more and more resources (i.e. money) to keep it going. Currently, our software company, Humankind Systems, is paying the bills. But BookCrossing is only approaching 10,000 members. When we have 100,000 to 500,000 members (not that far off), we'll need a dedicated staff, and dozens more servers, and extreme bandwidth and storage requirements, etc. etc. So if we don't plan *now* on ways to "monetize" the site, whether that's from publishers, or a corporate sponsor, or additional merchandise sales, etc., then we're doing our current membership, which expects this site to run forever, a disservice. We've made the decision that BookCrossing is FREE and ALWAYS WILL BE for the members - and the flip side of that coin is that we must find other sources of revenue. And that means marketing, long-term. Which I hope, in a round-about way, answers your question. :)