Is e-mailing more like "writing" or more like "talking"?

The Pew Internet in American Life Project released a fascinating report last month on "Teens, Technology & Writing" that concluded, "Teens write a lot, but they do not think of their e-mails, instant and text messages as writing." As a writing instructor, I wonder about the implications of this -- especially whether I'm fighting an uphill battle trying to get students to hold e-mail messages to the same standard as formal writing.

My argument for formal e-mails is that students need to learn to express themselves in many modes, in order to meet the expectations of various audiences. You don't communicate with your friends in the same mode that you use with your family members or bosses or teachers. Writing to people such as the latter -- who are in a position to evaluate you (e.g. fire you, give you a bad grade, deny you an interview) -- in an informal mode seems immature and irresponsible.

Sure, sometimes e-mails are sent from handheld devices and feel more like a text message than a letter. And instant messaging happens in the same place as e-mailing (say, in Gmail) so I can see how people could equivocate the two. But it seems better that students err on the side of being too formal than being too informal, especially with people upon whom they're trying to make a professional impression.