According to the National Association of Realtors, there are 7 million vacation homes in the U.S., and 16% of them (1.1 million) are offered as vacation rentals at least part of the year. If you're one of these homeowners and you're not getting as many bookings as you have in the past, the Internet could be the reason.

That's because instead of poring over classified ads or browsing the glossy catalogs put out by rental agencies, people all over the world now search the Internet and use vacation-rental Web sites to look for properties.