The upgrade from a first-generation iPod touch to an iPhone 4 is a significant one, in many ways.
If you haven’t seen the iPhone Retina Display, it genuinely is as good as the marketing suggests. No matter how close I hold the device to my eyes, I can’t make out individual pixels; the rendering of text is the best I have seen on any pixel display.
Other than the excellent additional hardware features of the iPhone, like the camera, GPS capabilities and of course, having internet access wherever I am, the other biggest upgrade is the sheer speed of the device compared to the first-gen hardware. The responsiveness of the UI on the iPhone 4 is as good as, if not better than, that of the iPad. Everything about the interface is fluid, responding immediately and directly to what you do. All the apps feel so much faster and it makes using the device a lot more natural when you aren’t waiting, even for a quarter of a second, for the next screen to load.
I’m very pleased with this as an upgrade to my mobile computing.