I have found “find folks via gmail” feature in twitter, linkedin, facebook, and plaxo quite powerful and, as Fred Wilson described, inherent in social networking. To me, the situation is, in a way, the gmail database being utilized (exploited?)by other platforms especially facebook, which is a threat and do not nesecacrily benefit to Google.
Yet it is a trurism that gmail in particular and email address in general is the engine of social networking platform. It might not be a win-win situation for Google and other platforms.
A few days ago, I just realized this feature is disabled in all the platforms I use and, according to twitter, due to a change in gmail contact system.