This New York Times article has the first data I've seen about how ineffective NSA's indiscriminate data vacuuming is, from 2009. I really doubt it's much better today.
"Crunching just one month of N.S.A. cellphone data, a secret report said, required 120 computers and turned up 8,615,650 “actors” — apparently callers of interest. A similar run using three months of British data came up with 24,760,289 actors."