I think that all of these (or at least most of them) are reasonable ideas that could work. I think the biggest problem is that a lot of them are either technica

I think that all of these (or at least most of them) are reasonable ideas that could work. I think the biggest problem is that a lot of them are either technically difficult or involve entering crowded markets. For example, the Craigslist killer can and has worked. The guys at RentHop and AirBnB are both attacking pieces of Craigslist's functionality. The problem is that most nerds don't have the ability to pull these ideas off. Heck, most people in general don't have what it takes to build a successful company. There's a big difference between hacking on something for a weekend and building a company out of it (although you can't build a company without starting somewhere). Overall, a lot of people (including many successful YC Founders) start out with stupid, unfocused ideas, and morph into something that's focused and solves a problem that people need solved. It's all just part of the process - if you wait for the perfect idea to hit you, you might never get started.