There is no penalty for having the same IP. What you need to know is the Google is a registrar, which means that even though you use private registration etc they still have access to the real information.
Google has stated that they do not use the database to actively look for you or penalize sites. If you are doing wrong though they now have an easy way to find all of the associations.
It is going to get a lot tougher on those who perisist in using techniques to manipulate engines with garbage. It will be easier for those of us who are actively creating unique content and working toward providing a resource of value online for our businesses.