As anyone who has purchased anything on Amazon.com in the past knows, once you start buying (or even just browsing their site), they start "consumer profiling" you. They want to know what you look for when you're shopping online, so that they can point you towards other items you might be interested in but didn't think to look for yourself.
This is good in principle, I suppose, if not a little creepy. Of course they do this by trying to match your shopping patterns up with similar people shopping on Amazon. Say Jimmy-Bob in Texas buys Season One of the West Wing on DVD, as well as a Black & Decker toaster. And say several other people do the same thing. Suddenly Amazon sees that I've bought The West Wing on DVD, and what do they start recommending for me? You guessed it, toasters. What does the West Wing have to do with toasters? About as much as Joan Rivers has to do with "natural beauty". But Amazon's magic consumer profiling algorithms will make the link and suddenly think it's all related.
The example I just gave was fabricated, yet typical of the types of things that happen. But to give a real example, Amazon also looks at what you buy, and recommends similar things that you might be interested in. About a year ago, I bought a new video cable on Amazon to connect to my TV. I just needed one cable and decided to buy it online since it was cheaper. Now, however, Amazon thinks I'm a connoisseur of fine video cables or something. Not a month has gone by where I didn't get an e-mail advertisement from Amazon for some cable (even the same as the one I already have, perhaps I need another?). When does the madness stop?
The big question is: does it work? Have I bought something on Amazon that I didn't realize I needed until Amazon pointed it out to me? Yes. I'm sad to say it's true. Probably for every recommendation that completely misses the mark, there are 3 or 4 that are dead-on accurate. I guess nothing's perfect, you just notice the few inaccuracies far more than the majority of the correct ones. And maybe -- just maybe -- it's time for me to buy a new toaster.