Christopher Allen looks at the Sizes of groups in a fascinating article which I've chopped into interesting chunks, below. Read the whole thing: The Dunbar Number as a Limit to Group Sizes

Lately I've been noticing the spread of a meme regarding "Dunbar's Number" of 150 that I believe is misunderstanding of his ideas....This all leads me to hypothesize that the optimal size for active group members for creative and technical groups -- as opposed to exclusively survival-oriented groups, such as villages -- hovers somewhere between 25-80, but is best around 45-50. ......In my experience the smallest viable group size seems to be somewhere in the range of 5 to 9.  ...In my opinion it is at 5 that the feeling of "team" really starts. At 5 to 8 people, you can have a meeting where everyone can speak out about what the entire group is doing, and everyone feels highly empowered. However, at 9 to 12 people this begins to break down -- not enough "attention" is given to everyone and meetings risk becoming either too noisy, too boring, too long, or some combination thereof. [via Life With Alacrity]