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.
You follow a canonical link to the resource, get a real page back, with real links, but js click handlers to enable AJAX-goosed speed for those with javascript enabled? And given that they imply a fallback for those times when javascript fails, aren't they actually better?
And GMail is a bit different than Twitter. It handles inward-facing data; content that no-one particularly wants crawled and wouldn't benefit much from caching.
Unless you want your URLs to look like twitter.com/someone#!someone_else, you're going to have to take the multi-step page load at some point when you transition from the HTML version to the AJAXy one.
Admittedly, you need a modern browser for that. But you can always present full-page-load HTML to users with older browsers and then provide AJAXy history-ified goodness to everyone else.
But Gmail is a webapp, not a website. You don't get a link to an email stored in Gmail. You can only access things once you're already inside.
Twitter is very different. If you're signing in yourself to update your own feed, that's one thing. But when you are trying to view the feed of someone else, that's a horse of a different color.
The question really is: should Twitter be an "app" or a "site"? If you allow links in from the rest of the web, it should be a "site".
Which sucks, because I frequently end up "launching" it by clicking a link to a Twitter profile or tweet on another site, so every few minutes I have to wait for the entire thing to load - and I often end up with a dozen tabs containing the Twitter app when all I really wanted was a few hundred bytes of HTML containing a single tweet!
Even with the assets cached, there's still an 8-10 second loading time (I just timed it). Compare that to a static HTML page showing the same content which would probably load and render in under a second.
Yea, in this case HTML/HTTP is being abused as wrapper around an app written in JavaScript, which loads and manipulates the content you see in your browser.
