You can't judge an entire breed of dog by few experiences...

There were 3 labs in the basic obedience class I took. One was a complete spaz hyper dog, one was very calm, intelligent, and well-behaved, and the other was a bit of a mix between. None were aggressive.

Like Aly said, you could have dogs from the same parents raised in a different environment and act completely different. This is the same with any breed.

Labs are popular, and unfortunately they are bred entirely too much. I swear if you look in the newspaper around here at least half the ads are for lab puppies. Overbreeding leads to dogs not bred for temperament, health, etc. and ends up creating some individuals with traits that are not desirable, and therefore, not a good representation of the breed. Just because a dog looks like a lab does not mean the dog has the personality a lab should have.