What exactly constitutes "personally identifiable" is a very complex issue -- almost anything can be personally identifiable with enough data processing or in combination with other data sources.
The judge and Viacom are the guilty parties here, trying to blame google only distracts from that fact. These are the same people who are working on laws that will mandate ISP logging, allow them to search your laptop and iPod at the airport, etc. Google keeping or not keeping logs isn't going to help you -- it's just running from the problem.