If you think it's bad on the iPhone 4, imagine how bad it is on a 2 year old Samsung Moment running Android 2.1. I've spent a lot of time trying to make basic touch interaction halfway responsive on older phones (read: anything but the newest phones), and all my efforts (which include trying jQuery Mobile, Sencha Touch, and jQTouch, as well as a bunch of from-scratch CSS and JS work) have been met with failure. I've concluded that, if you really care about and are paying attention to the details of user interaction in your app, the current state of native-feeling web apps just isn't there yet. The issues I've encountered are split about 50/50 between slow JS/rendering performance and non-standardized DOM event behavior.