I know that Comic Sans is generally the target of most font-based internet scorn. But maybe Impact is the truly insidious font—at least if you're interested in preserving ink. Designers Matt Robinson and Tom Wriggleswort explain how they came to this conclusion:

A selection of the most commonly used typefaces were compared for how economical they are with the amount of ink they use at the same point size. Large scale renditions of the typefaces were drawn out with ballpoint pens, allowing the remaining ink levels to display the ink efficiency of each typeface.

The process:

And the results: