Prof. Clay Shirky onces wrote that the best social software applications are those applications in which the social network effects are a welcome side-effect of selfish persuit. The most known examples are del.icio.us and Flickr. You archive your bookmarks on Del.icio.us and through the act of bookmarking you become part of a network of related bookmarkers and taggers.
Myriam Verschaeren sent me an e-mail entitled: "heaven! web2.0 tailor-made for me". Heaven in this case is librarything.com, a web-based social software application in which you archive the books you own and the books you've read. The site has some kick-ass ajax behind it: the moment you start typing about a book or author you know, it starts pinging the Amazon.com library and it offers you titles that match your query. The consequence of this is a Del.icio.us like universe in which you can jump from books you like to books you probably will like too and from books you like towards books that other readers of this book liked as well. This is soooo web2.0.