Attentiv provided some analysis of meetings:

• The average meeting costs $338, in terms of people’s time.
• Meetings most frequently begin at 11am.
• The average meeting has nine people in it.
• On average three of those participants will feel like the meeting was a waste of their time.
• 10% of all meetings last longer than four hours.

See other details, and take in some charts over here.

Source: Attentiv