Currently I'm using AllConsuming for books, del.icio.us for bookmarks and Morten's FOAF hosting to grab my wishlist from Amazon.
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As these services allow me to take away my augmented data in an easily processable format (XML/RDF) it means that as a hacker I can do Cool Things. But, more importantly, as an end user I don't have to worry about the pointy brackets: I key in some data and as well as an enriching my online experience, it also gives me a URL, a RESTful access point to my data, at which I can point other services. This is the Unix pipe metaphor extended to the web: small specialized services that can be plumbed together to create interesting applications.
Lost Boy: Scattered Self
Read the whole article. Some good usability comments, and at the end a"series of recommendations for building user-centric services".