Use a cutting board... (Score 1)

I spend 3.5 hours a day working on a train (I commute from Philly to NYC). The best solution overall after many different attempted solutions is a half inch thick plastic cutting board, available at your neighborhood grocery or kitchen supply store. Odds are good you can find one the exact size of your laptop. Nice and grippy for your rubber laptop feet, plenty of room for fans to operate, insulating enough to protect the jewels. If you leave that at home, I find a SkyMall/TrainMall open to the middle page laid over the lap is passable in a pinch.