Social networking is an interesting one. I enjoy Goodreads and I like that I can use it to keep a record of my books, make reviews and check out others' books and opinions, and maybe make friends that way. I'm not sure how much I want that to be integrated with a reader/app/bookstore. I've never set up the social networking side on any of my devices. I do take the point about Goodreads probably launching a store soon.
I think the other thing about social networking is that it seems to promise a solution to the so-called "discoverability" problem. However my experience has been it's generally no better (nor much worse) than the other attempts to solve this problem. I don't think we're there yet on this but I think whoever first solves this problem is probably going to make a lot of money. The thing is it's really two problems - the reader wants an effective filter but the seller wants a promotional tool.
Anyway that's a big topic but I think what I'd like is a better way to discover new books that I might like given the massive over-abundance of choice, but that I don't really believe that anyone has that yet.