spe is right on the mark with this
From personal experience, I filed change od address with CSC on 12.17.01 (faxed to CSC). i filed my 485 in July 2001.
I checked a week later with IIO, who confirmed that the address change has been done on their systems.
However, in January I got EAD and my wife\'s FP notice at the old address. That is not to say that INS always messes up. There are many instances where CSC has correctly forwarded the mail. But there is always a chance of screwup.
If you absolutely have to do the address change, it is preferrable to have someone you know stay at the old place (or make friends with them), so he/she can forward your mail to you.
soi