But once you do launch it, everything is faster than it would have been if you were performing full page loads at each step. For sites you "live" in, the application route makes a lot of sense. This is the way GMail works and people seem to like it a lot.

Unfortunately, web applications and web pages are growing increasingly divergent. It is simply not feasible to take the performance of web apps to the next level without doing away with full page loads. This is why Facebeook, Twitter et al are going the #! route. That's the cold hard truth.