Unfortunately the USCIS will not normally answer questions about the status of cases unless there is a problem, in which case you should get a notice about the problem, or if it is outside normal processing times by more than 30 days (which effectively just adds 30 days to the normal processing times).
There is no regulatory requirement that you remain in the U.S. while the re-entry permit is pending. However, the procedures for collecting biometrics essentially demand that you do.
The next action you should see is an appointment notice for biometrics collection (fingerprints and photo). After you have completed that appointment you can normally leave without worries. I have done several of these lately, including one for a client on the west coast. That application was filed on June7, 2010 and I still do not have a biometrics notice for the case which is in San Francisco.
If there is a legitimate need for an expedite, then you can apply for one with the Service center.
You can also leave until the appointment and then come back in for the appointment, but that is expensive. It also subjects you to additional scrutiny by CBP and so except in emergency situations I advice my clients to wait for the biometrics appointment before leaving.
The instructions for the I-131 form are found on page six of the instructions.
Since you did not do this the USCIS advises that you contact them through the 900 number and ask for instructions on filing an expedite request.