If you load up Gmail within Safari on your iPhone you should find the scrolling a lot more responsive in the inbox and conversation. But what has really caught my eye is the new fixed toolbar design. I really liked Gmail’s floating toolbar back when it first came out, but it would sometimes get stuck halfway down a page or get lost right up at the top, so it’s nice to have it anchored to the page for easy access.
[Incidentally, for the jailbreakers amongst us, might I recommend Fullscreen for Safari to free up just a little more space? It's $1.99 on Cydia and it allows you to see Gmail on the iPhone in full screen glory, among other things. Smexy.]