My I-140 (professional with advanced degree) was finally approved after 14 months of waiting. I initialy filed it in Oct, 2002, got RFE in Nov. 2002, sent back respone in early Dec. of 2002, and then waited, waited, waited... It finally came today.
We called customer service center a couple of times and filed electronic inquiry about my case three times, but the response was meaningless and useless. On the third time, the customer service rep. connected me to an immigration officer at the back end. She told me that once a case asks for more evidence, it is not bound to 150-180 days of approval time limit any more. So the lesson learned from my case is to submit as much evidence as possible when turning in your application. When I initially filed my I-140, I just turned in the evidence requsted on the instructions of I-140. It was proved to be insufficient, that's why I got an RFE and waited 8 months more to get approval.