ps19-
If you went abroad on AP, You can come back using the AP document. My I-485 was approved in the middle of my vacation and I had no problem coming in using the AP that I had.
minisantu -
I would advise you NOT to use your AP to go abroad since it becomes invalid (alongwith your EAD), once your I-485 gets approved. Now You have to have the physical card or temp GC (I-551) stamped on your passport. Leaving the country without either of the two, you will have a lot of trouble getting back in.
Hope that helps.