Here's a counter-example to this idea. I made justoneclubcard.com a few years ago. I think it's a clever idea and useful to a lot of people. I even get emails all the time from people telling me how great they think it is.<p>But it is rare that people spread the word to other people i.e., very little traffic comes from email websites, small blogs, or directly typing in the URL. Instead almost all of the traffic comes from lifehack type websites discovering it and linking to it.<p>So in my case I don't see the specific p2p type word of mouth he talks about. I think that only applies to certain products where you actually want your friends to use the same product as you e.g., "dude, you've got to get a myspace account".<p>What do you guys think?