Swanson - 11:03 pm on Jul 10, 2011 (gmt 0)
Panda is an extension of the strategy to create loyalty to Google.
Give users lists of sites that are "trusted" - more brands, more recognisable lists of sites that are familiar, more confidence in the results. Favour sites that fit with the profile of "good" sites - equals more satisfied customers.
More trust in the results, more trust in Google.