It varies tremendously. I've noticed with more mainstream stuff the lines seem worse. People get there pretty early and more closely together and it creates a backup. Getting there a bit early for those is good. I don't agree with another comment that you need to get there before first opener though, never seem it be THAT bad. Hippie jam band shit, people roll up whenever and it's more staggered. Some acts prompt a much more invasive search protocol it seems. These are just general points, it really does vary.

I will say I've gone to the National on average once a month or more for almost 11 years and things move a lot faster than they used to. Rarely is the line as long as it used to get and the process is more efficient, even with the metal detectors. That may have even helped in some ways, as I rarely see pat downs anymore.