Here are some experiences with regards to my entire track from NIW I-140 petition to I-485 approval. I had somewhat of an unique case, so if anyone here is in the same boat, this may be of help to you. I have done the entire process by myself, without an attorney, and long hours of research in the law library on U.S.C. Section 8.
Arrived to US in 1991 on J-1, not subject to section 212e, changed to F-1 on arrival. Became an H-1 in 2001 and filed for NIW in March of 2002, case was backlogged due to 9-11.
NIW was based on the "homeland security" with 18 letters of recommendation from U.S. government agencies, university, defense and legislative branch. Extensive documentation (resumes, Ph.D. diplomas, bibliography and sample publications) were submitted with an application.
RFE for I-140 for "statement of the qualification of alien" and copies of "all scientific communications in last 5 years" as well as "cross-referenced bibliogrpahy search listing applicant as a 1st or 2nd author." USCIS is insitutionally biased against NIWs, so it seems.
I-140 approved on 03/10/03.
Filed for I-485 on 4/11/03, RD: 04/23/03, 1st FP: 02/29/04
RFE on 07/11/04 for: Empl. Verification Document, 3 Years of W-2s and 1040s, Affidavit that J-1 was not subject to section 212e (two year home rule), Original IAP-66 from 1991 (keep all your documents!), Copy of university transcript and diploma, letter from the government agency stating that NIW scope of work is still applicable and copy of every page from any passport used since 1991 (copy your passport!!).
RFE docs received by USCIS on 08/10/04
Response that I-140 was re-adjudicated (?!!) and re-approved (?!!) on 09/01/04
Finally, E-mail and status change on 09/24/04 that the case was approved on 09/23/04. Still waiting for the paper notice.
Apparently stamping in the local office is a quasi-interview, where they take a last parting shot at you, until you file for the citizenship. Some folks have been asked to provide documentation establishing their legal status upon stamping of the documents.
According to a legal expert here in town, a great majority of I-140s are re-adjudicated before the final decision on I-485 was to be made, even if they were previously approved.
Hope this helps!