Speed mostly, but also the camera, ability to customize, widgets, the screen and hardware, the android 2.1 operating system, the many Google apps such as Google Voice and Google Goggles. I mean there are clearly some UI advantages that the iphone has where the equivalent in android is a little frustrating, but overall I think this Nexus One is a million times better than the 3G. I'm not talking about the iPhone 3GS, which I never owned. I'm comparing the Nexus One to my iPhone 3G.