My wife (US citizen) and I (conditional green card holder) are temporarily living overseas until the end of the 2007 since Jan 2006. Neither of us are in the military. Before we left the US, I had obtained a re-entry permit (conveying my intention to return back to the US), which is valid until Jan 2008. I have made more than half a dozen trips to the US in the meantime on business.

My conditional green card expires Aug 24, 2007.
We sent in our I-751 on July 9, 2007 to Nebraska Service Center with delivery confirmation (old service fee of $275). We included a copy of the re-entry permit in the package.
The package was delivered on July 15, 2007.

However, we haven't seen any activity since then. The check has not been cashed, and we have not heard back from the USCIS. Is this normal?
Since there is only 20 days until my green card expires, we are growing very worried.

We are concerned whether applying with a foreign address on the I-751 application is a problem, and whether the Nebraska Service Center is the right place to send (our last US address was in Illinois).
Also, what happens if I don't hear from the USCIS before Aug 25, 2007. Will I be able to enter the US?
IS there anything we can do in the meantime to know more about the status of our application or to expedite the processing?

Thanks in advance for your thoughts/answers.

you did the right thing, but the re-entry permit was issued with the wrong expiration date. The date should have been Aug 24 2007; the date your CR expires.
USCIS has received a lot of petitions lately. Your "delay" is likely caused by that... (since the check hasn't been cashed either).
I must also say that I haven't heard that USCIS would send NOA to foreign address. I was in a similar situation, but wrote US address on the form.

Thanks a lot for your reply, jula! If the USCIS typically does not send the NOA to a foreign address, how do we ever get the NOA? Is there a way of providing a new US address having already mailed the I-751?