I've had labs my whole life. I've also had a Chesapeake Bay Retreiver, Golden Retriever, English Springer Spaniel and currently an English Setter. I've always had multiple dogs, but one has always been a lab. Most of my dogs have been hunting dogs. Some have not, but that was when I was younger. I love labs, and they're great companions, as stated.
That said, you need to do your due diligence when you look for a breeder. To add to what Bluejazz said, the breeder should be offering a guarantee with the dog that it will not only perform, but have no chronic or congenital/genetic health issues. A good breeder should be willing to take the dog back if it has problems. Not only that, but if the dog doesn't work out, or the dog doesn't integrate well with your life, a good breeder should be willing to either take the dog back on a foster basis pending finding a new home, or they should directly help you locate a new home for the dog. Good breeders will always care about the dogs they breed and sell. They know their name is on it, and they do care about responsible and ethical breeding.
Additionally, there are some good breeders who also have mandates that potential buyers must fill out an application, and they must be approved either through interview or reference. They ensure that the dog owner isn't irresponsibly buying the dog as a gift for a child, or buying a lab to live in a 600sq ft apartment while the owner is gone 12hrs at a time or is enfirmed and can't walk the dog, etc. They make sure that the dog will have a good home and a responsible owner that is deserving of the dog.
Another consideration should be the size of the dog. Some labs are 60lbs and lean and sleek. Some labs are 85lbs and block-headed brick shithouses. Some labs are 120lbs and sleek and come up to the waist of a normal adult. Each one is different, so be aware of what you want and find a breeder that offers what you want.
Negatives:
Labs are energetic. Keep in mind that they're sporting dogs, so they're going to have a lot of energy when they're young. As they get older, they get lazier and much more manageable for people who like more mellow dogs. Sometimes you'll get a dog that is pretty mellow early on, but sometimes you can get a dog that is hyper for years. Part of this is how the dog is exercised and trained, but not always. Labs are the naughtiest and most energetic in the first 2-3 years, but tend to calm down after that. For those first couple years, you will have to be willing to spend more time with the dog if they are not used for hunting or tracking.
This increase in energy makes them get bored easily. If they are left alone, this can be a problem and manifest itself in chewing. Shoes, table legs, furniture, anything made of wicker, childrens' toys, and other items will all become chew toys if the dog gets bored enough. This is partly a training issue, but it's also associated with boredom. Keep that in mind.
I have taken in a lab from someone several years ago because they bought a yellow lab thinking that he'd be like other labs and would just be a happy-go-lucky couch potato. Problem is that the dog was still a pup and the owner was in over their head and wasn't realistic from the start. The lab is a sporting dog, pure and simple. They need to be doing something. This is why teaching fetch is important. They are retrievers, so they have instinct to retrieve things. If you foster this correctly, the dog will be a lot happier because they will have a sense of purpose. Sporting, working and herding dogs all flourish when they have a job to do. Something as simple as fetching/retrieving, or some kind of field training is enough to satiate a lab.
I'm personally done with labs, and my next dog will be a much calmer breed. Wife and I are at a point in our lives where we don't want any more high energy dogs. The amount of energy labs tend to have in their early years is a bit much. We may consider adopting/buying a started dog from a breeder. That's a good way to get into a lab without putting up with the really hyper early times. However, labs are really damn cute as puppies, so you miss out on that.
Oh, and don't fall for that Blue Buffalo/Blue Wolf natural food bullshit. That's what it is- utter bullshit. The food is not propertly tested and certified, and it's selling based on a premise that other dog food is bad or evil. Several companies have come out with their own variation of "natural" food to tap into this market, but realize that in the end, it's snake oil. I've talked at length with several veterinarians who absolutely hate Blue Buffalo/Blue Wolf because of how disreputable it really is. A lot of dogs are getting sick and dying from eating that crap. Google the Consumer Reports complaints on that stuff; it's sickening.
Don't go the other end and buy the cheap-shit 50lb fodder from your local farm and fleet store, either. Most foods are okay, but if you go with the higher quality foods, you'll be in a good place. Hill's Science Diet is the most recommended brand I hear about from all the veterinarians I know. Other good brands are Purina ONE, Purina ProPlan, Iams, Eukanuba, Royal Canin and a couple others.
I feed my dogs Hill's Science Diet. Well, one has to have Hill's Prescription Diet GastroIntestinal Formula from the vet, which is like $80/fucking bag... It's a good thing he's my buddy.