Actually there are a lot of problems with Amazon Recommendations, but I want to mention a few that really annoy me. If you're too impatient to read the whole thing, the brief summary is that Amazon has ruined any credibility their recommendations might have by seizing on any connection, however insignificant, to something I've bought/rated/wishlisted, and by failing to consider correllations with items I've rated low. Their credibility would be better if they recommended fewer items with greater accuracy, but Amazon's strategy seems instead to be to recommend as many items as possible.
1. The only things I have ever ordered from Amazon are books, music (on CD), and movies (on DVD). Nothing else. I have never ordered any games or game consoles, I have not ordered any Blu-Ray or HD-DVD movies or players, and I do not have any of those items on a wishlist. So why on earth does Amazon keep recommending those things for me? I don't own an XBox (or XBox 360), a Playstation (or PS2, or PS3, or PSP), a Wii, a Blu-Ray player, or an HD-DVD player, so even if I really did want a copy of Bioshock (recommended for me because I added brown men's dress shoes to my wishlist?!) it wouldn't do me much good. RECOMMENDED FOR AMAZON: Give users simple checkboxes to select formats they are interested in. If you notice a user buying something in a different format, suggest that the user might want to add that format.
2. One rated item or wishlist addition spawns dozens or scores of recommendations. I added a Green Bay Packers Cheesehead hat to my wishlist, and got recommendations for "cheese can cooler", "Green Bay Packers #1 Fan Foam Finger", "Cheese Erasers - 10 pack", "Cheese earrings" (I've never bought earrings from Amazon, my ears aren't pierced, these are women's earrings, and my wife isn't a Packers fan), "Cheesehead (Youth size)", etc. Similarly, a positive rating for one Steven King novel ( The Eyes of the Dragon) led to recommendations for dozens of King's novels. RECOMMENDED FOR AMAZON: Be realistic and cautious. If you have recommendations for me that are only based on a single item that I rated, bought, or wishlisted, just give me the one recommendation with the strongest correllation.
3. I don't have a child, and I don't generally like "children's films" or "family films". I do like Tim Burton and Johnny Depp, however, and I told Amazon when I bought Charlie and the Chocolate Factory . All of a sudden I started getting recommendations for all manner of children's films. These ranged from Cinderella (despite this film's status as a "classic", I have little interest in Disney's bowdlerized version of this story) to Barbie as the Island Princess. By the time I mark that I'm not interested in five or six such movies, Amazon should geet the clue and stop recommending them. RECOMMENDED FOR AMAZON: Don't just consider correllations among highly rated items, consider correllations among items I've rated low or told you I'm not interested in.
4. Telling Amazon that you own a movie leads them to recommend other versions (wide-screen, special edition, etc.) of the same movie. Some collectors might want every possible version of Harry Potter and the Sorcerer's Stone, but I'm satisfied with just one. Similarly, if I tell Amazon that I don't want the wide-sceen edition of The Santa Claus 3, I also have to tell them I don't want it in full-screen, Blu-Ray, HD-DVD, PSP, etc. (see also #1, above). RECOMMENDED FOR AMAZON: Have some sense. Don't make me rate movies more than once, and don't recommend another version of a movie that I've told you I own. If you want to really get things right, you might consider integrating the ratings I've put in the Internet Movie Database (which you own) into the Amazon recommendations.