[tomf64]

This is somewhat anecdotal but with the latest iOS and Facebook app versions, Facebook doesn't even show up on the list of apps that have requested to use my microphone. Unless they found some exploit to bypass Apple's restrictions and use my microphone without even asking for permission, I seriously doubt they're listening to users.

[bhouston]

In this case the guy admits there is no permission request granted, thus Facebook provably is not listening in on his device.

[olefoo]

Leaving out the possibility that Facebook and Apple have agreements that let Facebook bypass restrictions that other vendors are subject too.

Remember that Apple is not a government and can and does show favoritism in how it relates to developers selling through their system.

Although the prospect of Google, Facebook or Apple doing always on Voice Recognition seems unlikely in terms of bandwidth and power requirements.