updated version:
After you file N400 USCIS starts process by cashing check and initiating FBI Name check and Fingerprints, so once you got findgerprinted consider process launched. Only after FBI clears main (4) Service Center puts you in line for an Interview Date at your Field Office, once they find spot (ma take 2-3 month in busy offices, see step 3) and schedule your interview, your case is sent to Field Office and you receive your Interview Appointment Letter. After that procedues are very specific to Field Offices, some give you Oath letter right away, some send it 2 month later, so check with your Field Office's people's experiences only, don't read (or rehearse) just random or over 6 month old Interview descriptions.
1) Locate your Field Office by ZIP code here:
https://egov.uscis.gov/crisgwi/go?action=of....office_type=LO2) Find your Field Office's official processing dates (update usually on 15th of each month)
https://egov.uscis.gov/cris/jsps/ptimes.jsp3) Find people with close to yours Priority Date (PD) from your Field Office on this forum or others, for example this one has lots of Field Office specific info:
http://boards.immigrationportal.com/forumdisplay.php?f=184) wait until people with PD LATER then yours start receiving Interview letters, schedule Infopass - usually 2 weeks ahead, if still not received, go to Infopass and Inquire about case status - it may be
A. stuck on "Name Check" - then you are unlucky
B. "FBI Clear all checks and it's forwarded to Field Office , expect interview letter within 60 days"
either way go home and schedule another Infopass within 2 weeks - if no letter - schedule another Infopass in 2 more weeks,
if no letter within 4-6 weeks of fact that people who filed after you got their letters from your field office, start considering filing lawsuit against USCIS about delayed Name Check and read about it. your main document could be that that NOA1 gives you X amount of days and that is passed.
5) once you receive Interview letter - make sure you prepare for Civics and prepare to give evidence and clear confident answers for any abnormal parts of your application that could make you ineligible - it means within 3 (for US citizen spouses) or 5 years such things as: a lots of traveling, separate address with US spouse, job abroad, name change, oath word change, crime and legal issues, taxes, communism, terrorism etc.
6) if you happen to confuse Officer on Interview about your unclear eligibility, they may say "Approval pending" and they "need supervisor's approval of case", which may take another 2-4 month, but in this case you have much more right to file lawsuit - as your after interview letter states amount of days to expect decision.
Good Luck to everybody!
Good luck and keep us update please
Oh well...Hopefully soon!!!! 
together with a note of empathy to those who are still waiting 
very happy for you!!