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These numbers are only meaningless if you don't take into account Google's long term plan. They are combining all their services into a single product.
Imagine for a moment if you use Facebook email. Despite not using FB for social at the moment, when you write or send an email using @facebook.com you are part of the FB usage statistics, and rightfully so. The only difference is FB has this service already incorporated into a single product, its simply a feature. By extension then, in the long term, when Google combines all its services, regardless if you use the G+ element of Google, if you are using any of Google's services you are part of its usage statistics. To separate only the G+ usage would be like separating those users who use FB for games and those who use it to share photos.
So while its trendy to compare only G+ usage to FB usage, the big picture really will be Google usage versus FB usage, which means Youtube, Blogger, Gmail, Android, etc. Google's announcements merely contain that vision already.
3 years ago on Come On Google, Show Us Some Real Google+ User Numbers Already