In their paper titled The Aesthetics of Reading, Kevin Larson and Rosalind Picard present their findings on the effects of typography on reader mood and cognitive performance. They conducted two studies, each involving 20 people. The participants were divided into two groups of 10 and were given 20 minutes to read a specially typeset issue of The New Yorker on a tablet device. One of the groups got a badly typeset version (using Courier, with spaced out words), the other a properly typeset one.
Interesting findings. Bottom line: typography matters.