Your Governance Committee should consist of no more than 12 people and no fewer than 7.  It is often the case that as a committee grows in size it loses the speed with which it can make decisions. A governance committee that’s too small is less representative of the community of users and may make decisions that are not in line with SharePoint’s actual business uses.  A governance committee that’s too large is often subject to political agendas and infighting.  While there is no ‘right’ number of governance members to serve on your governance committee, realize that this committee’s success has more to do with personalities and corporate culture than it does the number of participants.

It is also recommended that you have at least 2 backup members that you can ask to participate in the event that some find involvement in the committee to be too time consuming.