I've seen it before, but I can't find it anymore. I think I remember Google mentioning that it would only be available in graphical form, but not data form, and also that it would only show one year, but I'm not sure. Did they ditch it? If not, where is it?
I emailed Dr. Varian, the chief economist at Google (formerly a Berkeley economist) to ask; he responded that the GPI was never intended to be a public project, data source, etc. It was simply a project internal to Google that got hyped up by the press. In my opinion (unconfirmed by Dr. Varian) Google, like virtually every other company, probably uses the Consumer Price Index (CPI) in their economic analyses.