Learning a foreign language, most people lack proper feedback from native speakers. Even if we have friends and teachers, always having to ask for help isn't very good. Lang-8 is a website that connects you with people who will correct your written entries (often very quickly). In return, you correct entries written by people who try to learn your native language (although not necessarily the same people who corrected you). There is an article about using Lang-8 for learning Chinese on Hacking Chinese here.