My limited experience so far echoes this. I'm in the middle of scratching an itch my wife has in such a way that it's useful to more people than just her, and part of that is a mobile application.

Sencha (and jQTouch before it) is absolutely gorgeous; I wanted very much to fall in love with it. On a webkit browser on my desk, it produced visually stunning results.

And then I tried using it with both an iPhone 3G and a G1. Yes, they're old tech, but they're the hardware I have on hand right now to test on (and not exactly uncommon in the field), and performance is abysmal.

I would assume the same tests run against an iPhone 4 or an HTC Evo would blow me away, but my wife has a G1, and I'm building this for her first. :)

visit www.gmbhnews.com from your iphone/android/BB to see how it looks as a webapp in a field where you mostly find native apps. It may be a bit difficult to market mobile webapps from my experience, since peoples don't use search on their smartphones (I think, this stateent is from Steve Jobs), but it's definetly worth it. and you can still create a native app , if it's really the point, and target a specific platform.