I just noticed...
Feb 28 2014 difficulty = 3,815,723,799
on Feb 28 2013 difficulty = 3,651,012

That's a 1,000+ times increase, so a 1 TH/s miner today is only mining as many bitcoins as a 1GH/s miner 12 months ago.

Over the same period the bitcoin price has only increased about 20 fold (~$30 to $600).

Let's hope this rate of increase doesn't hold up for all of 2014, or in 2015 we'll be looking at ~0.004 BTC/month from a 1 TH/s miner!