It's essential for web browsing on a touchscreen. To accurately tap links on the screen without one you have to zoom right in, then you can still press the wrong one and end up paying twice for things or canceling an order or something. With the trackball you can zoom around the page straight to links and press it in to select. Again something the iPhone doesn't have which is overlooked in reviews, but is a definite requirement. Being able to finger-gesture your way zooming in and out helps a bit but without that you need absolutely need a trackball.

@ Richard Drysdall : The video is actually fine and is as good as can be expected. Just something else this review has wrong.