For the next version of Gmail, one of Google's goals is to get it to load in under a second. They stated that for them, "Speed is a feature". I couldn't agree more. It's something that Google seems to take seriously in most of their applications. Their user interfaces are pretty minimal, but they're fast. Sure, they could focus on adding other features, improving the design, making it look like a desktop version, but instead they focus on speed. I'm a bit torn here, as I love a beautiful interface. I've tried Mobile Me, and it's really nice looking, has all the little details that Apple gets right, but damn it feels slow after using Gmail. If I had to make a choice, I would choose Gmail every time.
For the next release of your app, I'd suggest try to make increasing speed the top priority. I for one would love to see the release notes for a new version that just said "Improved performance by 2x all around". I know it's something I'm going to start focusing on in my apps.