David Mc

No prizes for the largest tree, but there was a mention in a press release: http://ir.ancestry.com/releasedetail.cfm?ReleaseID=688295

1,578,421: The most records attached by a subscriber, Bonnie Myers of Lynden, Wash., to a single Ancestry.com tree.
404,611: The number of "nodes" or branches on the largest subscriber-created Ancestry.com tree. The subscriber, Paul Rhetts, of Albuquerque, New Mexico, has used Ancestry.com to trace his family history back 20 generations on each side.