In an online world where Web sites run million-dollar commercials during the Super Bowl simply to introduce themselves, it’s nice to know there are some sites that can gain a devoted following through old-fashioned word of mouth. Well, as old-fashioned as the Internet can be.

In March 2001, Ron Hornbaker was admiring the PhotoTag.org site, which tracks disposable cameras let loose in the world for anyone to use. He already knew about the popularity of WheresGeorge.com (which tracks American currency by serial number), and it got him thinking of what else people might enjoy tracking.

He realized no one had yet started a site devoted to tracking books, and about a month later, BookCrossing.com was born.

BookCrossing is the act of releasing books “into the wild” and following their journeys.

BookCrossing members (membership is free) register their books at the Web site, so each has its own ID number, which is used to “tag” or label the book inside the cover.

They then leave the book somewhere others can find it, and the label inside explains itself to whoever picks it up.

That person writes a brief note on the Web site using the book’s ID number, ideally after reading it. Then they pass it along to a friend or release it into the wild.

Each time someone makes a journal entry on a book, the previous releasers get an e-mail.

Thankfully, trading books is both legal and traditional behavior of book purchasers, so there is no piracy aspect to BookCrossing, as opposed to trading music CDs or other media.

Members trickled in at a relatively slow rate – 100 or so per month – until March 2002, when Book magazine published an article profiling the site. Since then, more than 350 new members join daily, and the BookCrossing experience has been the focus of numerous television, radio and newspaper features (now including this one).

The membership has grown to more than 110,000 members and more than 329,000 books registered. Much of that growth was due to word of mouth and what BookCrossing calls “word of mouse,” members using the Tell-a-Friend feature of the site.

Now, there’s even an International BookCrossing Meetup Day (http://bookcrossing.meetup.com) held in up to 545 cities worldwide on the second Tuesday of every month, where fellow BookCrossers get together to discuss their common love of reading.

If the current growth rate holds steady, nearly half a million people will be BookCrossing members in three years.

Of course, that doesn’t consider the possibility of a Super Bowl commercial.

If you’re interested in hunting down books released near you, visit http://www.bookcrossing.com/hunt.

Eddie Hargreaves was the webmaster of EastOregonian.com and EONow.com and now works for SacObserver.com. He can be reached at meged@earthlink.net.