Librarything versus Shelfari

I found Librarything to be a bit more formal than Shelfari, due mostly to its cataloguing access with "Amazon ,the Library of Congress and 78 other world libraries." Similar to Shelfari in its book club capacity, bookmarking favorites and networking, Librarything also gives a listing of discussion groups based upon subject, gebresm authors, etc., that can be viewed and/or joined by linking. LT also allows anyone to create a new group and offers tagging tips and additional library data on several of its blogs.