USCIS Email on 5/24/12:
Due to the high number of recently filed I-129 petitions with USCIS, customers may experience a longer than usual period of time to receive a receipt notice from USCIS.
Usually, customers can expect to receive their receipt notice within 30 days of delivery confirmation.
However, due to an unexpectedly high volume of I-129 petitions, it may be an additional two to four weeks before customers receive a receipt notice.
Customers who do not receive notification of receipt of an I-129 petition within 60 days of their delivery confirmation date may contact the appropriate Service Center via the email addresses listed on our Contact Us Web page.
This is a temporary situation and we apologize for any inconvenience this may cause.