TheRealCanadian nicely answered your questions earlier. I guess most of the answers you are seeking can be otained by spending some more time in searching/browsing this forum. Let me try to respond to your questions one by one. TheRealCanadian and others as well are welcomed to chime in.
1. Do u know any reason why they transfer the cases from Vermont to Nebraska. Is it because that I have been staying for a long while in Detroit or there could be any other reason.
Only the adjudicating officer who transferred your case knows the real reason. Guesswork from our side is immaterial.
2. What are the usual reasons why they transfer the cases from one center to another center.
Likely to be (though not guaranteed) any one or more of these:
http://www.immigrationportal.com/showthread.php?threadid=99990&highlight=jigesh
3. Recently when I checked up on the website it says that we have recived this I 485 application on december 24 and the process is usually taking some 540 days. I have already spent more than one and half years in vermont. Do u think that this could be a standard reply.
Yes.
4. Do u think I could be recieving a letter from Vermont that the case has been transfered to Nebraska and another letter from Nebraska similarly telling me what is going on.
You/your attorney should get a letter from VSC about transfer. NSC will write you/your attorney only if they either approve it and/or when they schedule an interview.
5. Do u have any experience why they could have transferred my case from Vermont to Nebraska.
Apart from response to Q-2 above, I don't have any experience. May be TheRealCanadian can add information/experience if any.
6. My sixth year ends in another couple of months, should I immediately file for H1 extension for the seventh year.
If the valid status is still H-1B, better to file the extension though you can use EAD and still be fine (I, in your place would file an extension).
7. I checked up with my lawyer and he tells me that he has seen such a thing happen first time for him and he wants to wait till some notification is recieved. What is the way to know to know whats is happening.
Transfer is not unusual. Basically, nothing serious should be happening to your case though I understand your concerns. If your employment is alright, and if you have all the needed documents, you should be fine. Said that, I don't know if there's any way (most probably, not) of finding out what's going on in case of an unadjudicated case (For an approved case, you can request your papers under freedom of information act FOIA).
8. The reason why I said local office means detroit because from the website I have seen that in many cases vermont has transferred to many local offices and me living in detroit and as detroit comes under Nebraska region, I thought may be VSC sends to local office through the approriate district office. Kindly read below the actual description available from the website----"" ON DECEMBER 20, 2003 , WE TRANSFERED YOUR I 485 application to Register Permanent Residence or to adjust status to an office in Lincoln, Nebraska for processing. That office will notify you when theu take action on your case. You should recieve a notice informing you that your case has been transferred to a local office."
Alright.
9. Do u have any idea when I can approximately anticipate some kind of information either from Nebraska or Vermont in this regard.
VSC should be writing you/attorney about transfer within 6 weeks typically. NSC will write when they schedule interview (don't know when) or ask for a re-fingerprinting (if expired).
10. Can you kindly advise me with some alterantives.
Alternatives to what? I don't see any option other than waiting for the interview [or opt for consular processing for visa interview in India, which at your stage of I-485, doesn't seem to me worthwhile. Discuss with your attorney or visit
http://www.immihelp.com/ and click on "consular processing" if you have any more questions in this regard. I am just mentioning this option purely from the theoretical point of view because I don't see any point in doing it at this stage of your I-485.].
Best wishes,
Jigesh
Disclaimer: Personal non-legal point of view only.