I have a few myself. The person who wants to befriend me has to have something in common with me to be accepted. If it's a reader or a reader and a fellow book blogger who shares my taste in books I always accept the request. If it's a author who thinks I might enjoy their book based on the books in my Goodreads shelves or an author I've read before I'm accepting the request. That being said there I sometimes have to turn down a request or two. When a person wants to be my friend on Goodreads and they have 5000-6000 friends I'm suspecting that that person is just there to collect friends(unless it's a very popular author). If the person shares many of my books I consider him/her but if we have nothing in common i reject the friend request. The same thing goes for adding friends, I'm only requesting to be added if we have something in common.
I'm sorry but I'm not on Goodreads to get the longest friend list, I'm there to discover new books from people who likes much of the same novels that I do. Of course it is not necessary to have identical tastes(that's not what I'm saying, that would be dreadfully boring), variation is good and that way we might pick up a book we never ever would have read it it weren't for the recommendation from one of our Goodreads friends.