I also thought this was pretty cool. Two artists--Matt Robinson and Tom Wrigglesworth--decided to take some of the most commonly used typefaecs and see much ink each uses when drawn at the same point size. The artists drew large scale versions of the fonts with ballpoint pens and then measured the level of ink each took.
Kind of awesome!
Garamond is the most efficient, while Impact eats the most ink. Helvetica and Times New Roman are both in the middle of the list.