Viral Loop: From Facebook to Twitter, How Today's Smartest Businesses Grow Themselves

Here's something you may not know about today's Internet. Simply by designing your product the right way, you can build a flourishing business from scratch. No advertising or marketing budget, no need for a sales force, and venture capitalists will flock to throw money at you.

Many of the most successful Web 2.0 companies, including MySpace, YouTube, eBay, and rising stars like Twitter and Flickr, are prime examples of what journalist Adam L. Penenberg calls a "viral loop" -- to use it, you...