I love my retina display.
Yeah, there is no comparison to the old screens. I looked at a friend's 3G - so slow and so pixelated and dark compared to my new iphone4 - it's easy to get used to it, and impossible to go back to the old screens.
All those old 3G's and 3GS's are going to be dirt dirt cheap. Good for experimenting with, and kids toys. I love it! Just think how cheap those will be in another 2 years, and what you could do with them. It's awesome.