The lack of standardized metrics is problematic and ought to rectified. But as an advertiser, I don’t focus on a social network’s total number of users or whether they’re “active.” I focus on the specific users I’m targeting. After all, microtargeting is what separates Facebook ads from Google ads.
To wit: I care less about how many people use Facebook—whether actively by logging in or passively by being checked-in—and more about how attractive Facebook is for, say, cat owners to whom I can market litterboxes.
To be sure, the former metrics are helpful when deciding where to spend your dollars, but ultimately I judge the success of a campaign—and base my decision on whether to do it again—on its results (impressions, click-throughs, and conversions).