I am shocked to come across you post - I was seriously bitten by a female black lab that I had known for years before the incident. Like you, I was under the impression that all (or most) Labs were non-aggressive.
It is possible that people may be seeing more temperment problems with Labradors since they are a very popular breed. As popular dogs, many are being bred by people who might not be the most conscientious about genetics.
In my specific case it seems the dog was not mentally stable due to inbreeding and she was IN HEAT (duh!! stupid owner...). She attacked me as I was walking away from her. A few months later she jumped out of a moving truck and died. She was a normal, intelligent, sweet dog during the first few years of her life, something just "snapped" when she was about 3 years old.
I have a Pharaoh Hound/Pit Bull mix, so I am accutely aware of the "one bad apple spoils the bunch" theory about breeds, so I'm very cautious of thinking that Labs are all going to turn vicious.
I would definately see what you can do about this particular dog in order to protect yourself, even if it means calling the police or animal control to knock some sense in to the owner.
Good luck!