According to the NSA, yes: (S//REL) Tails: Complete Bootable OS on CD for anonymity - includes Tor (S//REL) Adds Severe CNE misery to equation (Thanks to a famous Tails user for providing these documents.)
Bruce Schneier, December 2013: What do I trust? I trust, I trust Tails, I trust GPG [...] I don't use Linux. (Shhh. Don't tell anyone.) Although I have started using Tails
Userbase
broad and diverse
Challenges
Cadence
preparing a release takes 6-10 solid days of work
new release every 6 weeks + a RC 1-2 weeks before
Popularity
in July:
11.5k boots a day (doubles every 6-12 months, since years)
35k downloads of the OpenPGP signature of Tails ISO
⇒ increasing expectations
Limited resources and time
mostly volunteer work
2000 commits, by ~10 persons, on the last 6 months