I found this article on the dangers of email quite interesting. I turned off my auto-download feature a long time ago, so I'm not worried about wasting "8 1/2 hours a week figuring out what [I was] doing moments before" my email chime went off.
However, I did find this paragraph eerily true:
Tom Stafford, a lecturer at the University of Sheffield, England, and co-author of the book Mind Hacks, believes that the same fundamental learning mechanisms that drive gambling addicts are also at work in email users. "Both slot machines and email follow something called a 'variable interval reinforcement schedule' which has been established as the way to train in the strongest habits," he says.
Basically, we check our email like frantic, trained chickens, because every once in a while, in between the junk mail and the ads for enhancing our sex lives, we get a good reward like a funny story from a good friend. The slot machine keeps us coming back, and drains our time bank in the process.