The applicability of "long-tail" content applies beyond UGC, into applications and programming languages themselves. 37signals has pushed the industries' thinking around building applications fast with Ruby on Rails. It feels like Merb will push that even further.
It's time to push the programming language abstraction down the stack though. It's a solved problem (probably solved years ago, but now w/ RoR and Merb, it's _really_ solved).
Sure building out functionality quickly matters, but if you're going to succeed you need uptake, and uptake equates to scale. Your application needs to be able to scale. Twitter's a great example of being built in no-time at all, yet stumbling with scale.
Scale remains the real problem. The brains that know how to scale win. The brains that can build functionality fast will become commodity (probably have already).