An interesting post from Murthy's o8/25/03 chat :
Chat User : My visa is an L1A. I filed for a GC under EB1. Labor exempt. I-485 was filed over 180 days ago. Can I change employers?
Attorney Murthy : The BCIS has recently seemed to turn around on its position on these types of cases. Originally, they had mentioned that AC21 portability will apply to all employment-based cases. Now, they are saying it differently in AILA meetings. It seems unfair, since the purpose of AC21 was to ensure that the employee is able to switch employers and has the freedom of movement as if the person was a permanent resident if the BCIS takes longer than 180 days to process the I-485 case. Also, of course, the I-140 EB1 case should have been approved. Otherwise, there is a bigger risk of the entire case being denied, even under present AC21 interpretations. The safe course is not to switch employers until we hear one way or the other.