It moves a lot faster between pages that don't require fresh data because it uses database storage on the iPhone and Android's built-in Google Gears implementation, which supposedly makes it work better on a slow connection besides giving it some offline powers. Search and loading emails from the main screen isn't necessarily quicker, but picking contacts and opening particular messages within a thread—yes, threaded conversations work just like real Gmail now—is definitely quicker. You can also get to other Google apps (like your calendar, which is improved now too) in a snap.
If you don't like it, you can always go back to the old site, too. [Gmail Blog]