I was just looking through the teams - there are some huge ones! The largest has accumulated 13,815 years of processing time. I think that's pretty amazing.

Here's the link:
http://www.grid.org/services/teams/team.htm?id=270E60B7-EC7B-4389-BA40-8C473D6C5A5B

The largest vehicle-related team seems to be for the Subaru Impreza owners. They have about 397 members:
http://www.grid.org/services/teams/team.htm?id=4B4667E4-95B8-4747-800F-F7E54398A3C2