I have to say that I too am guilty of letting mine get very low. While I have great intentions of stopping and getting gas, the next thing you know, I'm on bone dry. I think the most I've put in is 30.8 or so. Now it is true that the fuel pump uses the gas for lubrication, but I have no idea what the actual danger of having it that low for a short period of time is. Now if you really want to scare yourself, those of us with 32-gallon tanks, go look at your actual tank.
It is like 15 feet long (exaggeration), but seriously, it is amazingly long. It really makes you wonder how much gas it takes just to cover the bottom of that tank 1/4" deep. Maybe that's where a gallon or so goes? Makes me nervous every time I have to go up the long incline just to get to my local gas station.