I have a lab, Jack, who is from show lines. I wouldn't call him laid back exactly, but he has never been a dog to need over 2 hours of exercise a day. Labs that are great family dogs get that way through proper training, guidance, and outlets for their energy. Jack is 8 and goes swimming weekly year round, plays with our other dog, and goes to the dog park regularly.
Jack really was not a nippy puppy, but we was taken from his litter at 10 weeks, so that may have had something to do with it. Sally was a year old when we got her, and she had more of an issue with play biting then he ever did. They are mouthy in that they LOVE to carry things in their mouths. Jack never greets us without a toy in his mouth. Labs are also pretty notorious for eating the inedible as well--Jack has eaten 4 socks and a pair of my underwear. I know many people who have had their labs eat everything from children's toys to soap to rocks, so keep that in mind when dog proofing the house.
Also, they shed like, a LOT. If dog hair bothers you this is not the breed for you.