I'm experienceing the same problem. Like my Xinhuan said it is a issue in the latest patch.
Try to logg out first and then go back to the login screen - and then exit WoW by hitting the "ESC" key, this work for me. Trying to exit WoW by pressing the "exit game" button freezes my WoW client.
This happened to me tonight as well. I could log in, but combat or camping kicked me from WoW. I ended up deleting my folders and I am currently rebuilding my UI. I now think that wasn't necessary after reading this thread. Oh well, I am excited to start fresh!