Honest Tea has set up unmanned booths in cities across America, with a hidden camera pointed at each. You can watch the live footage and see the stats at:
Honest Tea
Pretty interesting. I'm sure that the numbers will fluctuate, but it's nice to see that about 90% of people are still being honest about it.
EDIT: Some of the thefts are hilarious, though. Like this guy:
He filled his arms with bottles and walked off.