Well I got mine last night (Desire) and i love it. I've not got a 3GS, but compared to my iPhone 3G it's rapid, web pages etc were loadingso quickly (quicker than my mates 3GS too, but I expected that seeing it's got new hardware etc, i'm sure the next iPhone will be just as quick if not quicker).
My plan was to have a play with it for a few days and decide if I was keeping it, but I knew the second I switched it on it was a keeper. Screen is awesome and the widgets are great too. Would reccomend it to anyone.
I was going to keep the iPhone too and use it as an iPod but I might aswell selling it an get a 2nd hand iTouch or get a Classic. The desire has got a very good media player on it, but as I noticed even with the iPhone 9 times out of 10 when i'm listening to music via earphones i'll be doing something which means I can't use the phone functions anyway (cycling, gym etc).