When we first visited BookCrossing.com two years ago, the fledgling online community had 3,400 registered members and a driving force, Ron Hornbaker, who saw the site as a pleasant diversion that might become an effective calling card for his software development business.

Today BookCrossing boasts 257,000 members, 10 million page views per month and 1.1 million registered books. It has also become Hornbaker's full-time livelihood.

Who knew? . . . Not Hornbaker.

"We're getting 400 new members a day, and that's on an increasing pace, so it looks as though we'll have a million members within a couple of years," he says.

Not bad for a diversion.

BookCrossing.com is for book lovers who would rather give their favorite titles to total strangers than toss them on a shelf or in the trash. Members "release" their books "into the wild" - they simply leave them in a public place - after registering the titles on the site and affixing stickers that explain what's going on. The stickers include a unique identification number that lets the books be tracked. The person who finds the book is supposed to note the sticker, become curious, visit www.bookcrossing.com, report the ID number and log a journal entry about the find. The site also provides forums for members to swap tales.

Paying for such an operation - never mind a small staff - has proven challenging but not impossible.

"When it started growing we had to figure out a revenue stream," Hornbaker says. "The problem with the sites that take off without some sort of funding is that they just implode of their own weight."

While T-shirts, promotions and partnerships with book publishers have generated some income, BookCrossing's best source of revenue has proven to be "release kits" that provide members with the eye-catching labels they need to attract a passerby's attention to their books. Membership is free, as are more rudimentary labels, but these kits that start at $18 apiece have proven to be a hit.

"We get 400 new members a day who are pretty excited about joining BookCrossing, and half of our sales go to new members on day zero," he says. "With a quarter-million people it doesn't take a very large percentage to be buying things to keep a small team like ours in the black."