I had two concerns just over a year ago with leaving my Palm Treo 680 for the iPhone. One, how was I going to do going from a physical keyboard with plenty of tactile feedback, to a touch screen with none? Two, how was UI responsiveness going to be?
Physical, tactile, UIs are generally a requirement for me. "Touch screens" usually suck, but, I've gotten over that hurdle with the iPhone. The benefits (and new UI gestures) outweigh the issues; I've adapted.
iPhone firmware 1.x releases abated my fear around UI responsiveness. Contact lists loaded fast enough, and text input fields acquired cursor focus fast enough. My fear w/ the initial iPhone rev was unfounded.
I've been using the iPhone 3G with the 2.x (yes, the latest update as of this writing) for awhile now, and I'm utterly disappointed with the UI responsiveness at the OS/UI framework level. The waiting I have to do at text entry fields (iTunes password prompts, contact search entry fields) has negated the speed increases that the 3G network provides for data transmission. Net-net, I'm still wasting the same amount of my life waiting on the device to do something, that I was on the old first gen network and 1.x firmware.
The only reason I bought the new 3G device was for increased network data transmission, because I wasted too much of my time waiting for email to download, and web pages to load. While that issue has been resolved, I'm now wasting all my time waiting for client-side UI elements (namely entry fields) to accept input. Sad.
I suspect many/most Blackberry users will avoid the iPhone based on this issue alone.
Please fix it Apple.