You've probably heard about the costs of task switching in terms of breaking concentration, preventing thought flow, and the like.  Typically we think about external interruptions like phone calls, people asking questions, going to meetings, etc but what about all the self-inflicted interruptions like email, IM, SMS messages, etc.

Well there's a new thing added to the list called Twitter (or software for twits as I think of it) based around the idea of keeping people up to date on what you are doing right now. Pointless but popular, a great distraction and a top class way of preventing you from doing anything useful.

Creating Passionate Users has a more in-depth article about this and it's well worth the read (make sure to check out the links in the article as well).