I have been waiting for 26 months since my original application for naturalization.
I sent my N-400 form back in March 2006, got my FP done within three weeks, and went for an interview in early May, 2006, which I passed except that my name check was not completed. Then nothing from USCIS for nearly two years. I called the Service Center many times, went for an Infopas at least 5 times, wrote to the senators, first lady, etc - the response was always the same (when I got any response) "name check is not completed." Then in response to my recent status update request, USCIS sent me a letter that "my name check has been cleared" as of 4/11/2008 and that I should be now expecting my interview letter (although I already had my interview in 2006). Within a week or so of that letter, I got second FP appointment on 5/3/2008 since my original FP done in March 2006 were experied. When I went yet for another Infopas just before my second FP, I was told that if I already had the interview, I would not be needing another. But then who knows?
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You are almost done... it will be just matter of days now. I can feel your pain what you have gone through. Good luck!