I really like the iPhones I've had. In addition there are other smartphones I enjoy using. If Apple offered the now very popular 4.0" or 4.3" display, like my EVO, Droid X, and Galaxy S have, I'd use my iPhone 4 as my primary smartphone.
Once you use a larger display, the 3.5" iPhone display does feel tiny when responding to emails & forums. I use smartphones quite extensively and greatly prefer a larger display. The argument that many use "it'll make the phone too big" fail to give Apple credit for their design capabilities. Apple could build one with an awesome 4.5" display and keep it relatively small, more so than any other company. It's a fact.