1) No, it's not. In most states if you are driving below the speed limit and there are a certain number of cars behind you (in WA it's 5 or more), you are required by law to pull over and allow the other vehicles to pass. You can, and will, be issued a citation for "obstructing the flow of traffic" if you are driving below the speed limit with cars backing up behind you (even if they're following at a safe distance).
2) Yes, it is. Mostly on multiple lane roads though. Even if you're in the far right lane on a freeway, speed differential is a major cause of accidents. Even more of a cause than simply exceeding the speed limit. If everyone else on the highway is going the speed limit and you're going 10 mph under, you're creating a speed differential that is inherently less safe than if you were moving with the flow of traffic even if everyone is paying as much attention as possible.
ZV