While this made me feel creeped out at first, that “metadata” all seems like the public information that we intend to share when we signup for a service like Twitter.
Systematic collection and archiving of "metadata" is not the same as data being available at some point in time. (It's really the same as the arguments against other automated surveillance: it's "public metadata" where your car is on public roads, but a country-wide database based on automated scans is still different than the fact that someone can follow you around manually)