Jill Walker has an excellent post on the issue of "hardcoded privilege" in her blog today. (Alas, Tinderbox doesn't support Trackback, so this won't be a bidirectional link. I'll post a note in her comments pointing this way.)
In it, she raises the issue of the growing information aggregation based on Amazon (daypop, allconsuming, etc), and the privileging of amazon that results. She raises it in the context of the impact on smaller bookstores, but that's not the part that scares me.
What I don't like is the narrowing of the information pipelines, and our resulting dependence upon the goodwill of the pipeline owners. Recently, I've seen other people commenting on the danger of treating Google as a public information infrastructure, and the same holds true here.
What happens, for example, if Amazon decides that they don't particularly want to include books on a particular subject in their collection? It's their right--they have no public duty to carry items on their virtual shelves. But if they become the de facto sole source for books on the 'net, it's only a matter of time before that happens.
I don't know what the answer is. But it does make me wary of services that reify this monolithic structure, no matter how seductive the services they provide may be.