It really depends on what I'm doing.
If I'm browsing the Internet or playing a one handed game, I lean to the left and rest my head on arm which I prop in with my arm rest.
If I'm playing gmod, CoD, BFBC2, etc, or typing, I sit pretty close to the way you "should" sit at a computer.
If I'm playing WW2 Fighters, my face is inches from the screen.