Great podcast, only confirmed my purchase for S,S & S.

On screens I use a screen, but often role in front of my players. Mainly in dire situations, mind you. But the effect is nice. If we are doing combat, and an adversary misses, they love it. They'll hoot and holler. Taunt me, and just enjoy the small roll victory, until I critical one of them in the open. Then it's "ah crap man, no fair!"
Depending on the fight, or social situation I take rolls in front of the screen or behind it.
But then again I try to be fairly transparent.
I do however do like Zachary. I place my mini's, notes, maps and other "hidden" stuff behind the screen to keep those suprises... well surprises for my players.

I think the big thing is, and will always be in home games, know your players.
In a con game, I think a looser set of playing might be in order, but use what you as a GM feel most comfortable with.