Justin Krueger, Nicholas Epley, Jason Parker, and Zhi-Wen Ng write (pdf):
Without the benefit of paralinguistic cues such as gesture, emphasis, and intonation, it can be difficult to convey emotion and tone over electronic mail (e-mail). Five experiments suggest that this limitation is often underappreciated, such that people tend to believe that they can communicate over e-mail more effectively than they actually can. Studies 4 and 5 further suggest that this overconfidence is born of egocentrism, the inherent difficulty of detaching oneself from one’s own perspective when evaluating the perspective of someone else. Because e-mail communicators “hear” a statement differently depending on whether they intend to be, say, sarcastic or funny, it can be difficult to appreciate that their electronic audience may not.
The pointer is from Sendhil Mullainathan on Twitter.