We are about to do the same thing. My hu*****and's (primary applicant) and my daughter's I-485s were all approved in September 2006. I sent my RFE for I-485 (marriage certificate) in the beginning of October 2006 and was told a decision would be made within 60 days. However, till today there is still no answer. This delay also resulted in a delay of my renewal of EAD. We think this is USCIS's fault and made an appointment with local immigration office to talk first.
Thanks a lot for telling your experience!