sfgirl - 8:56 pm on May 15, 2011 (gmt 0)

Bill also did an analysis of Google patents that shows some of the stuff they have the ability to look at (and how they could potentially use it), like:

copying and pasting (site engagement metric)
bookmarking (site engagement metric)
time on site (site engagement metric)
links clicked (site engagement metric)
mouse-hovers in SERPS
lots of user-based probabilities in ordering results