Unquantifiable Risk
A lot of the Web 2.0 startups getting started these days are of the variety where their risk is completely unquantifiable a priori. Mostly, these are highly social applications which require a large group of people to change their behavior slightly or to adopt a new behavior to work. The list includes peer-to-peer lending, social networks for recommending things, new group communication systems, downloadable photo sharing clients, etc. More