While 8-10 people is the industry standard for an agile team, and many agile consultants tend to suggest that there is an optimal team size, the truth is that agile parameters are relative. What's good for a large team would be abnormal for a smaller one. VersionOne's David Walker recommends a range between 5 and 15 team members depending on the size and needs of your organization.
David Walker is the Director of Product Marketing at VersionOne. In this presentation he discusses scaling agile, optimal team size and how this changes for distributed teams. According to Walker, teams should be able to modify processes and parameters according to their unique situation.