About a year ago, I posted about the effects of group size. Here are a couple of interesting links on that very topic: here and here. From the second article:
Your brain is hard wired to pay attention to about 150 people. Try to have a relationship with any more than that, and your life will turn to pure crap. Just ask the Military, Gore-Tex, or Krippendorf's tribe. They'll all tell you the same thing. One-fifty is the way to go. They've known for hundreds of years that people work best in groups of 150 or less.