We were getting a bit nervous so we called up the USCIS automated service line, which informed us they had sent out a "Request for Further Evidence" (RFE) to our primary fax number. As we didn't supply a fax number (what is this, 1987?), who knows where that went. After a couple of phonecalls they'd posted the request out, refusing to give us any more details.
A couple of nervous days passed where we were wondering what they could possibly need that 960 pages of documentation we spent weeks preparing wasn't enough.
The letters arrived this morning, asking us to prove where exactly we'd spent $358,600,000 since entering the US.