Sorry Smarterthanu213, but I have to agree with alli_wan on this one. There are laws on many states' books stating that a driver may not legally drive slowly enough to cause a hazardous condition, but the case you describe doesn't seem to fall into that category. Going more than 15 MPH under the legal limit is the usual break point for police to intervene, and since this fellow was going close to that he should have pulled over to allow those behind him to pass, but I stop short of labelling his actions rude or dangerous.
Speeding is dangerous on back roads. While I understand the reasoning, especially on back roads that one knows very well, it only takes a single problem to cause a severe accident. Consider that while you're speeding down the road, that you encounter something that you simply can't avoid. For everyone who says that they react fast enough to avoid anything that might be laying on the road, I ask how you would handle coming around a corner to find someone oncoming in your lane, due to their making an illegal pass or swerving out of their own lane for whatever reason. In that case you can forget evading the accident at all, and then it comes down to what you're going to hit, and how hard you're going to hit it. Unlike a highway, there's usually very little room on the sides of back roads before you encounter hard objects like trees, utility poles and houses, and the difference between hitting something at 30 MPH versus 40 MPH is well documented.
In short, I'd say that if you're willing to exceed the speed limit on a road you give up the right to complain about other people driving at unusual speeds, fast or slow.