I usually use a "screen" to the side, mainly for the charts that are necessary so I don't have to go looking them up (presuming I'm using a game that needs charts). I don't like it between me and the players.
Of course, I generally do a lot of standing up and pacing about to run my games, which makes it a bit impractical. I also improvise a lot. I'll ignore rules in the book, especially if they get in the way of the story. When I get a rules-lawyer in the group, this will usually come up a time or two before I explain: Rule #1: I make the rules. I may (or may not) choose to use the rules that the dude whose name graces the cover suggested that I use. My prerogative.