Siri can help with your homework and maybe even tell a joke, but she can’t update your social network status. However, you can make this happen with a small workaround. First, sign up with the social network of choice for mobile updating. The service will give you a number to use. Add this number as a contact and assign it the website’s name (f. ex. “Facebook” or “Twitter”). Then tell Siri, “Message [website] [status].”
Siri will ask to confirm and will send it as a text message. With the linked account, Siri will use your message as a status update.