I don't agree with anything written in that article. Based on AC-21, you can change your job if your have an approved I-140 and your I-485 has been pending for more than six month. You can even become a consultant during this time before your I-485 is approved, which makes you yourself the owner of the approved I-140 not any other company.
I have friends and relatives who applied for citizenship recently. Based on my inquery from them, there is no question about how many times you have changed your job or even if you have changed your field.
And just another thing, USCIS has difficulty approving cases which have been pending for several years, do you think they are going to monitor how many times a greencard holder changes his job or goes to school or does anything like that?
Also, check this out, it clearly says that a greencard holder, has almost all the rights of a citizen except voting. check out page 8 and the rest if you like:
http://www.uscis.gov/files/nativedocuments/M-618.pdf
Please correctly if I am wrong, but based on these, I believe once you get your greencard, you are done with immigration until you want to become a citizen and there are other measures than employment for approval of citizenship.
Well....I am stuck with an employer for last seven years. I am paid extremely low no extra facility + hell a lot of other things...as they know that my GC is pending. I wonder if I can change the job without going through AC21. Someone told me that I can change my job without AC 21 since I have work permit and 485 is pending for more than six months. I heard the stories of ac21 that sometime they call for interview and so on.