AC-21
an interesting fact about AC-21 is that the trigger for I-140 portability is that
your I-485 must remain unadjudicated for > 180 days, not that you must change jobs after 180 days.
what this means is that, theoretically, you can change you job the very next day after your 485 is filed, and if it remains unadjudicated for 180 days, then your job change was validated retroactively! in the very unlikely event that the your 485 came up for adjudication before 180 days, then, of course, you are out of luck. it is for this reason that somebody wanting to use AC-21 portability will try to wait until 180 days are over before actually changing jobs - unless of course they were laid off, then they would not have a choice. but at least AC-21 offers a ray of hope in case of a lay off, when earlier there used to be none.
admittedly, this is a very liberal interpretation of AC-21, and it is a view espoused by the immigration attorney Carl Shusterman, as presented this website:
http://immigration.about.com/library/weekly/aa012902b.htm
also, in the absence of INS regulations, an adjudicating officer might fail to see it this way. so if one is planning to use AC-21 portability, then they should also enlist the services of a good lawyer.
please read up what Shusterman has to say on AC-21; more importantly, hire a good lawyer when your case comes up for hearing.
if you haven't applied for EAD with your 485, do so immediately. i wish you the best of luck in your job search.