I've been running a lot of games off of my laptop recently, rather than printing out the pages (and pages and pages) of notes that I usually generate on the relevant people / locations / plot points of any given story, which eliminates the need for a screen to keep the players from peeking. I do have a pretty awesome homemade Mage 2nd Ed. screen, and the homebrew CoC screen that I posted about last year is still in the works (delayed due to chronic laziness). I, too, like to have the reference charts handy, since it can be a major pain in the ass to look things up in the middle of a session if a situation demands a by-the-rules arbitration on something. I'm not really the kind of GM who feels the need to roll behind a screen because I don't like to fudge my rolls. If I'm rolling like shit, then the deranged killer in the giant battle mech just isn't going to hit the players with his chain guns.
Still, I usually like having a screen to hide my notes and to reference charts/rules. It's helpful like that.