You can be identified by how you type, even behind proxies and Tor. Protect yourself with KeyboardPrivacy.
Some websites are storing your typing patterns and it turns out that after some training, systems can identify who is in a system by the way in which passwords are typed. You can then be identified on other websites using the same underlying system. Paul Moore has created a proof-of-concept Chrome extension which changes the output of your typing to the website by randomising the rate at which the browser sends it to the website.