http://www.theregister.co.uk/2011/01/14/reading_fonts
Harder to read fonts showed better rates of recall in some studies. Interesting. Kind of wonder what teaching types think.
This could be useful in some situations, but overall, I'm skeptical. As LD said, any time you have something that requires more attention to learn (and receives that attention), you have better retention. I suspect that in very small amounts, a slightly-hard-to-read font would produce good results.
However, there's also an 'accessibility' issue here. After a certain point, you're going to get diminishing returns on a harder-to-read font simply because students are going to say 'fuck it' and not complete the task. In the setting this experiment has, the task was novel and had the advantage of every participant completing the task as norms. In a less controlled setting, upping the difficulty of reading something isn't going to produce more willing/focused students. It would probably just end up creating a bigger difference in retention between the good students and the poor students. The students who were going to complete the assignment anyway would probably improve slightly, and the poor students would simply not attempt it.
Relating my own experience using my foreign language study, I've found that I definitely remember the content of 100 lines of Japanese that I had to translate over the course of 30 minutes far more extensively than a quick 100-line passage in English that took maybe 5 minutes. However, after about 100 lines of Japanese, I tend to just start skipping passages that don't look important~
If I'm motivated, then sure, a slightly more challenging assignment will require more attention and thus produce more retention of content. However, accessability is one of the keys to encouraging motivation. So I really hope they don't start printing textbooks with comic sans font based on the dubious usefulness of this experiment... >.>;;