Short Line Lengths?

Paul Graham's essays are formatted to have short lines of around 60-70 characters per line. Jorn Barger has started writting posts using even shorter lines.

In his FAQ, Graham claims that "Text is most legible with at most 60-70 characters per line."

After reading these, I am starting to find longer lines too dense and less comfortable to read.

I'm haven't formed a definite view yet, but it's got me intruigued.

Is it actually better? Is the idea of 'making the most of' the window space something that will give way over time?