There is something definately not right in your case, Rick; otherwise it shouldn't be taking so long to wrap up your case...let alone when your application is said to be approved. I'm not saying that there is a complication in your case; rather I'm saying that your file is lying under the dust...for sure; otherwise I know so many people who were asked to take oath within 2-3 months later of their interview...and they were not even told that they were approved. For example, one of the persons I know who was interviewed at Garden city office on December 4, 2008, received an oath letter two weeks ago for this coming Tuesday. She was never told that her application was approved because she had two criminal cases in the past. She was kept calling everyday to check the status of her application but always been told that her application was pending.
She was interviewed after you and she had more complicated than you do. I think you should keep calling the INS on their 800 line and ask them to issue a inquiry status email to local district office. Believe me, once they will send a inquiry status email, you will miracleously receive an oath letter within 10 days. Of course, many officers will refuse to send that inquiry status email and will give you all kind of run-arounds, but don't be disappointed nor argue with them; rather call back and speak to another officer. I'm sure you will find an officer who will send this email for you to local INS office.
In NYC, oath ceremony is conducted at least 3 times a week and each ceremony contains 150-300 people...so how is it possible for INS not to find a slot for you since November of last year when your application has already been approved?? It's just not possible. Don't take no for an anwer; rather keep on the top for your own cause.
Good luck...