As I live in a tourist trap, several of the titles I've released (of other author's works) have ended up in the UK, Australia and the Ukraine. You can't buy publicity like that. Add to that the fact that good comments can always be pulled for the back cover before the official release date.
I have two novels coming out in a couple of months and I've already ordered a dozen advance reading copies from my publisher that I can "forget" in high-traffic areas of the city that I know the tourists frequent. I'm anxious to see where they end up.
I've also forwarded the latest newsletter here (with links) to several author's publicity and promotional newsgroups I belong to (several thousand members globally consisting of authors and publishers) so they can also see the great and inexpensive PR aspect of BookCrossing.Com
Any author that complains of "lost royalties" doesn't understand promotion or finances (typical royalties from a $5 book is less than fifty cents).