The Frontal Cortex blog at Wired has an interesting post about a psychology experiment in an Ohio school district that showed that making fonts slightly harder to read in a variety of classes improved long term learning and retention. The basic idea, called disfluency, is that the harder the brain works to grasp something, the more deeply it's ingrained and the easier it is to retrieve later. Changing the font a little in this experiment added that little extra bit of challenge that made the learning more memorable. The authors of the study, published in Cognition, say the trick to choosing the best font is to find the line between more-difficult-to-read and illegible.
This study demonstrated that student retention of material across a wide range of subjects (science and humanities classes) and difficulty levels (regular, Honors and Advanced Placement) can be significantly improved in naturalistic settings by presenting reading material in a format that is slightly harder to read. [C. Diemand-Yauman et al./Cognition]