Ajaxian has posted a ridiculously simple way to enable web apps to mimic the iPhone's side-to-side flicking behavior using custom CSS supported by MobileSafari. If you're creating a web app specifically for iPhone and iPod touch users, you can get a similar feel to a native application with MobileSafari.
MobileSafari includes some CSS 3 support, including advanced DOM selectors and support for animations and transitions. Chances are, other browsers will have limited support for CSS 3 draft standards, and whatever you write probably will only work in MobileSafari and Safari 3 on the desktop.
The test application in this movie shows how it tracks finger movements across the screen, and performs actions based on the distance "swiped." Very nifty.