What Are We Doing That Makes Us Stupid?

We do it once per week, sometimes more. We do it in a group and most of the time, it's unproductive and a waste of time. What is it? 

Meetings don't just eat up your time at work. New research shows that meetings actually make us stupider. I like how the story said "stupider" as if to imply we're stupid to begin with, but I digress.

Working in a group makes people perform poorly on intelligence tests because some members in the group are so worried about doing well on the test that they actually divert their brain power from the test to maintaining social status in the group.

The study leader, Read Montague says that we may joke that committee meetings make us feel brain dead, but the study's findings suggest that meetings actually make us act brain dead as well. Test group subjects went to a meeting and then were given an IQ test that they had to take in front of a group, and there was actually a significant drop in IQ, especially when the IQ results were shared with the group.

How many meetings have you been to that were actually productive? How many people should actually be in the meeting so it is productive? What is the ideal length of a meeting?