Amazon has acquired Shelfari , a site where people can share their reading lists, review books, and find books to read. Others have noted  that Shelfari sports a cool user interface, but I note that there are quite a few book list sharing sites out there like it, such as LibraryThing , aNobii , and GoodReads .
I’m not sure that the UI alone is really enough to differentiate Shelfari from the pack, particularly if Amazon over-commercializes it. I think if it tries to push book sales too much, it might easily disaffect the usership and they could easily swing over to one of the handful of competitors.
Amazon has been extremely adept at seeing the potential value of social media, and have been bullish at integrating it. Yet, some of their aggressiveness at pushing their commercial products has seriously degraded the social media value of some of these initiatives. I have more commentary on specifics of this which I’ll share later.
A number of large internet companies have gone the acquisition route to try to combine the benefits of social media into their existing content and commercial sites. Thus far, it’s not entirely clear that this strategy works longterm, because the commercialization of social media sites tends to irritate users and makes their users take a cynical view about their involvement. A notable exception to this is Flickr , a photo sharing site which Yahoo! acquired and which continues to grow in popularity and usage.
Google also sees the potential of book reviews and sharing of reading lists — I recently blogged about how Google added shared reading lists  for politicians and pundits.