I am not going to comment on AL's policies or the perceived "invasion of privacy" which some have voiced. I can, however, give you a contractor's point of view, although it is probably not all contractor's opinion. I will put this in the context of a tile contractor since it is the only perspective with which I am familiar..
I have spent years building my business and reputation. This, if you think about it, is a very tenuous juggling act. If a customer has a great experience they will tell the next person that asks them about their experience with your company. If a customer has a negative experience they will tell everyone they know and everyone they don't. This is why I feel AL is a benefit to both contractors and clients, it allows the good to get out there as well as the bad. As a contractor, however, you are never guaranteed the good reviews, even if you have hundreds of them. They are rarely put out there for prospective future clients to review in a non-biased medium. You are, however, guaranteed the negative reviews, always. Remember, clients will tell everyone about a negative experience.
As a contractor I always have this in the back of my mind, I work endlessly to make certain my clients are absolutely happy with my services. Whether or not the client is a member of AL is irrelevant, there are thousands of places on line and off where a negative experience can be posted. Any respectable, responsible contractor knows this.
Example: the last time you sat with a friend and asked them about their auto repair you received one of two answers. "I took it to so-and-so and they got it fixed." or "I took it to so-and-so and they messed it up so badly, I'm so upset I don't know what to do" Which one of these answers do you think turns into a ten minute conversation? Which one is going to permanently burn the mechanic's name or company into your brain? It won't be the first.
If you have a problem with a contractor the first step, of course, is to take it up with the contractor and attempt to get it resolved. Any responsible contractor will do what they can to fix the problem - always. If they don't then they deserve a negative review in my opinion. Stuff happens - always. Contractors are human and at times certain circumstances will create unforeseen problems. A contractor's honesty, reliability, and integrity should also be measured by the manner in which they handle complaints or problems. I feel this to be a very reliable measure of a company. I can go from feeling questionable about a company to feeling incredible about them by the way they handle a complaint. It can also go in the other direction - quickly.
That said, a large amount of responsibility is laid upon the client to decide whether or not to post a negative review, although many do not look at it like that. It is incumbent upon you, the would be client, to try to weed out the viable negative comments from the overreactions simply because a lot of people do not think before they post something they may later not feel as adamant about. Or they post something negative without even attempting to contact the contractor or even thinking before doing so. I'm not saying that negative feedback is always bogus, it isn't. But it sometimes can be.
The best thing to do, in my opinion, is to ask the contractor about it. If they tried everything they could possibly do to make the situation right and still couldn't then you can make your decision on that. Judge the way they answer the question. Do they explain what happened clearly and what they tried to do to make it right? Or do they get upset, badmouth the client, put the blame on everyone and everything else? This is a great indicator for you about whether or not you feel you can trust the contractor. The ultimate decision lies with you, the client.
I look at complaints as opportunities to further impress my clients. That is exactly what they are. Every contractor gets complaints, the measure of a company is how they are handled and resolved. Not everything can be controlled, different situations require different solutions and the ability to resolve these situations is what makes a particular contractor stellar.
For the contractors: if you have a problem or complaint - fix it. It's usually that simple. I have had to fix things that I've ended up losing money on but you can't buy a reputation. If you have a client that absolutely cannot be satisfied simply accept that and move on. I know they exist and you can only do so much. Just document everything you've attempted to fix the problem, calmly and factually explain that when it is brought up and show the documentation to any future clients that bring it up. If it was something that was out of your control the prospective client will realize that and it shouldn't have any bearing on their decision to hire you. If they don't realize it you probably don't want to work for them anyway.
For the clients: If there is a complaint against a company or contractor you are concerned about - ask them about it. The manner in which they answer will tell you more about them than hours and hours of research. Being concerned about a contractor receiving your personal information? That, to me, is a ridiculous argument - sorry. Any contractor with whom you've had legitimate dealings already has all the information AL will forward to them and probably a lot more. If you are that concerned with it then you have more problems than what AL will create for you by forwarding that information. It's probably something you need to take up with the proper authorities rather than AL. Let's be realistic.
As always - just my opinion. 
Roger
Tile and Stone Contractor
Fort Collins, CO
TileArtCenter.com