My parent sent out their application on Dec. 2006. Got a reply from the embassy today, that is very fast. They told me that the case is under process and did not say how long it will take to finalize. They also said they sent out a mail after they received the application with the file number in it. If my parents never receive the mail, they need my parents' updated address labels in Chinese and will send it again.
Thanks everybody for your inputs, especially cube1234!