Go on the USCIS website, look for the 'case status' link on the right, go to 'portfolio'. You can sign up , plug in your receipt numbers and your email address and mark the 'email enabled' tab.
For some reason it sends 2 emails for every action taken.
Once you are signed up you can anxiously stare at the 'Last Updated' field. It is meaningless, but it will give you another thing to worry and post about.