I've been using blippr for a while to record what films I watch, what music I listen to and what books I read, displaying the most recent in the sidebar here. However, I've found that it simply doesn't list a lot of the books I've read (films seem to fare better), and while you can add new items, it's a bit of a chore, and I've had one or two books that I just could not seem to add to the system.
I started looking around for alternatives, and came across LibraryThing. It may not be the prettiest site in the world (though it's not bad by any means), but it is really full of features. You can add books in multiple ways (the easiest of which is to type in the ISBN, or buy a cheap USB barcode scanner from them which integrates with the site), and it pulls in full details. There are no end of customisation options, including choosing which of the localised Amazon sites to pull information from^1^, and the ability to add books to different lists such as Currently Reading or Wishlist. The blog widget is also highly customisable, and I chose one showing my reviews.
The social aspects of the site are very impressive: it can generate recommendations, you can join groups with particular reading interests, and the sheer number of reader reviews (many of which are very detailed and thoughtful) provide a lot of scope for future reading matter.
Using blippr was convenient because I could log all my watching, reading and listening in one place, but LibraryThing just seems a better choice for my reading style. Though the short form 160 character reviews of blippr good in many ways because they are easy to write, it's sometimes nice to write a longer review, which you can do on [LibaryThing]. You can view my catalogue here, though it is currently rather small. I'm not planning on going through my bookshelves to add things, but I'll add new reads (and items to my wishlist) as I go along. If any of you are LibraryThing users, do let me know what your username is, because I'd love to look at your catalogue.
^1^ It may be borderline obsessive, but it irritates me when sites which find cover images pull up ones from US releases, because then it doesn't feel like my book, film or CD. LibraryThing can use a UK site so you are likely to get the right cover, but you can also easily choose alternative covers. Why yes, I do organise my CDs and vinyl alphabetically... ↑