One of the best things software development shops can do to improve productivity is to set Outlook to only check email once every hour (or 30 minutes at least).  This is because people tend to take quite a bit of time to get back to difficult tasks.  Email, and IMs, are difficult to ignore when that little "pellet dispenser" pops up on the lower left hand side of your screen.  And once your mind strays it's hard to get back on task.

A recent research project reported in the New York Times (link - free registration required), bears this out.  Here's the money quote:

In a recent study, a group of Microsoft workers took, on average, 15 minutes to return to serious mental tasks, like writing reports or computer code, after responding to incoming e-mail or instant messages. They strayed off to reply to other messages or browse news, sports or entertainment Web sites.

“I was surprised by how easily people were distracted and how long it took them to get back to the task,” said Eric Horvitz, a Microsoft research scientist and co-author, with Shamsi Iqbal of the University of Illinois, of a paper on the study that will be presented next month.

“If it’s this bad at Microsoft,” Mr. Horvitz added, “it has to be bad at other companies, too.”

So, turn off that email while you're coding!  (And driving!)