I was able to try out the phone where I work. WP8 runs just as smooth as wp7.5 does. I didn't see anything that stood out as groundbreaking between the two OS's. I was hoping we would be able to swipe to close current apps that were in a paused state, but I could not.
The phone looked nice, but still had that plastic samsung phone feel to it.
The volume, power and camera buttons all felt solid. However the home/windows button I did not like. It does not light up, so you cannot see the windows logo in the dark. Pushing the button was even worse, there was no click when pressed, instead it had a very mushy feel to it. I honestly had no idea if I actually pressed it unless it went back to the home screen. Also, the bottom edge of the screen was very close to the button that when pressing the button I would almost always hit the screen and open an app or hit something on the screen by accident.