If Google+ runs as deep as Google seems to imply it does, anyone using Google search while signed in is "using" Google+. I know when I do searches, I get results based on what people I know have been sharing. If I search for "putty", my top result is the PuTTY client, because lots of Google+ users have visited the page or liked it or shared it or something. I can see under the search result how many people +1'd it.
I'd consider that "using" Google+ the way I understand Google+ to work. You don't need to use it as a Facebook in order to experience the "plus" in Google+ (criticisms about SPYW aside).
Ok, but that definition still renders the numbers meaningless - it's just a box you happen to see forever onwards if you've ever said yes to one of their prominent enticements to find out what Google+ is.
If they told us how many Google+ members use those results, and how often they are picked in comparison to the non+ results, that would tell us something that justifies using that definition.
As it stands, the numbers only tell us how many people clicked through a very prominent ad.
I'd consider that "using" Google+ the way I understand Google+ to work. You don't need to use it as a Facebook in order to experience the "plus" in Google+ (criticisms about SPYW aside).