Saw this article here today, here's an excerpt:

Texts in easy-to-read typefaces make it harder to recall information than if it is presented in less legible formats, research suggests

A study by Princeton University found that a significant number of those tested could recall more information when it was presented in unusual typefaces rarely used in textbooks.

The research suggests that introducing 'disfluency' - by making information superficially harder to understand - deepens the process of learning and encourages better retention.