No Receipt for I-539 Application Filed Over 1 Month Ago?

I filed an I-539 B2 status extension application for my parents over one month ago. The check was cashed two weeks later, but we have NOT received a receipt for this case. USCIS.GOV shows that Canifornia Center is still processing I-539 cases with notice dates prior to 1/13/2007. So the actual processing won't take place until several months after my parents' current status expires, but that's fine, I guess. But should we have received the receipt by now?

Any experience to share? Thanks a lot.