Perhaps others are aware of this, but it came as a bit of a
surprise to me, since I rarely do packet dumps while performing
Google searches, but it seems that Google is correlating searches
with Gmail accounts - even if the user has logged out of Gmail.

In the course of performing some network and software testing, I
ended up going to Google and performing some basic searches to
ensure my network tweaks were functioning properly. I also happened
to be running some packet captures at the same time. While viewing
the packet captures, I noticed some odd parameters being passed by
my browser to Google - Gmail account information.

I thought I may have still been logged into Gmail, so I logged out
of Gmail and performed the search again, and again my Gmail account
was associated with the search. I then went into Firefox's cookie
configuration and deleted the Gmail cookie, performed the search
again at Google, and now my Gmail information was no longer
associated with the search.