In reply to Jason Brinkley.

Right. And the lesson goes beyond regression. Read this article on using transparency to overcome overplotting in a scatter plot. The same idea applies to density estimation.

Incidentally, this idea is not new. I first saw "replace scatter plot with a bin plot" in Carr et. al (1987) JASA, but that paper references ideas of Chambers, Cleveland, and McGill in the early '80s. And does anyone remember "Sunflower Plots" from the '80s? Michael Friendly implemented a SAS macro for sunflower plots around 1990.