I went from the Droid 1 to the Droid X, thinking I could get used to the on-screen keyboard. Boy, was I wrong. I missed the physical keyboard from day 1. So then I went to the Droid 3 and thought I'd miss that extra .3 inches of screen. The first day I noticed that the screen looked smaller, some of the text was smaller. But after that I got used to it and now don't miss the larger screen. I'm still getting used to the keyboard, it's different enough from the Droid 1 to throw me off every so often.
On the up side, I've found the D3 to be faster and more responsive than the DX. The app drawer scrolling side to side instead of up and down threw me off at first but I've gotten used to it and now it makes sense.
On the down side, when they keyboard is closed the D3 screen seems to rock a little big side to side, my D1 never did that. And I miss the physical camera button! And I wish I could turn off the way the screen shrinks when I go to drop something from the app drawer onto the home screen, and also the sliding effect that occurs when moving from one home screen to another.