I have a feeling Google was testing out the personalised search feature even
when you are not signed in.
They appeared to do something with cookies but only in I.E.
Not long ago I was seeing something very strange and initialy thought it was
case related, but after a few tests came to the conclusion it was cookie
related and personal search related.
Even though I wasn't signed on, Google appeared to know it was me when I
was searching and was returning my pages in favourable positions.
I tested again using Opera and FF but couldn't replicate what was happening.
Have a read here and see the screenshots for more about this,
http://www.uksmallbusinessdirectory....goings-on.html