I just grabbed one at Best Buy and have to say I was mostly looking at the lower screen the whole time. I almost prefer it was just the lower screen since I prefer handhelds
I also found myself looking at the lower screen more often...but I don't think it's because I actually prefer that screen. The heavy duty spring cable attached to the back of the controller made it terribly uncomfortable to hold at any reasonable distance from the TV.
I could tell the controller was light, but the cable's resistance was really detracting from the experience.