I'm in impatient but also practical person, and there's little else in the world that makes me more furious than being trapped behind someone abusing the left lane. On the one hand, it's simply annoying when you cannot go a preferred speed (the speed limit or faster) because some bastard is just hanging out in the left lane not passing anyone. But on the other hand, it also obstructs traffic and can be dangerous.
Traffic in the right-most lane has a greater likelihood of being sub-fast-enough because cars are entering or exiting the highway (ramps!). If a car needs to merge onto the highway, common courtesy (actually I think the law) demands you move over to the left lane to allow this newb onto the highway - this is impossible when some buttsack is parked in the passing lane and prevents you from moving over without dangerously speeding up or slowing down.
In addition, when people get trapped behind slow traffic in the fast lane they often become impatient and begin trying to pass on the right side of cars. This is also dangerous for the reasons outlined above - people may need to get right to get off the highway and even knowledgable drivers generally won't expect to be passed on the right.
The passing lane has the misnomer "fast lane." This is due to the fact that generally when you're passing someone it means you're going pretty fast. IT DOES NOT MEAN YOU CAN SIMPLY DRIVE IN IT BECAUSE YOU'RE GOING OVER THE SPEED LIMIT. If you're going 75 in a 70 zone but the traffic behind you is coming along at 80, you need to move over as soon as you can.
Also if there are people parked on the right shoulder, it's the law (as well as safe and courteous) to move to the left lane as you pass, if possible.
So please please please if you're not passing another car, get the GDF out of the left lane.