There has been some research done that shows that ugly fonts can make the reader retain more information. This is called "disfluent fonts" and it works by making the reader concentrate harder to interpret the font, and in doing so they remember the text more easily.
There has been some suggestion that text books should use fonts that are harder to read, in order to make students retain the information within.
And there have been some people that have suggested they should be used in e-readers as well.
Some links:
The Educational Benefit of Ugly Fonts
Why ugly fonts and messy handwriting make it easier to remember what you've read
How to Change Kindle Fonts, Disfluency and Memory Retention
So maybe we should be asking Kobo to install hard to read fonts on their e-readers?
