Many brilliant startups from a user perspective failed in the late 1990s and early 2000s as fundable business plans changed drastically from requiring eyeballs to solid revenue models. In the current funding climate, it again seems that an application that motivates obsessive use can be funded even if lacking an immediate revenue model, particularly with a new well-funded landscape of potential acquirers out there including Google, Facebook, Apple, and Microsoft.
Moreover, other conditions have changed. For example, advertising is more lucrative than it was ten years ago, providing a revenue model to startups that can generate eyeballs. Fulfillment and shipping are better understood for retail models (compare pets.com to zappos or diapers.com). Assuming my sense is right, I believe that it would be a fruitful exercise for entrepreneurs and venture capitalists looking for a business to systematically pick through the graveyard of failed 1.0 startups to find ideas for which there is a second life. And if someone can bring Kozmo or Urbanfetch back and make it work, you will make so many of us so happy!
