In a study last year, Dr. Thomas Jackson of Loughborough University, England, found that it takes an average of 64 seconds to recover your train of thought after interruption by e-mail. So people who check their e-mail every five minutes waste 8 1/2 hours a week figuring out what they were doing moments before.
I would suspect that Twitter and random IMs must double the wasted time leading to 17 hours a week of figuring out what you were just doing. This constant distraction is similar to gambling, heeding to a "variable interval reinforcement schedule" which is the same feeling you get from playing a slot machine.
"This means that rather than reward an action every time it is performed, you reward it sometimes, but not in a predictable way. So with e-mail, usually when I check it there is nothing interesting, but every so often there's something wonderful--an invite out or maybe some juicy gossip--and I get a reward." This is enough to make it difficult for us to resist checking e-mail, even when we've only just looked. The obvious solution is to process e-mail in batches, but this is difficult. One company delayed delivery by five minutes, but had so many complaints that they had to revert to instantaneous delivery. People knew that there were e-mails there and chafed at the bit to get hold of them.
As an interesting contrast, the NY Times published a piece earlier this week about the Brave New World of Digital Intimacy that helps to explain how all this connectivity actually might be making our lives better.
Today I am on blog, Twitter, IM, cell phone, and three different e-mail accounts...at least until I get to the casino.