Hey yellocard,
Hang on to your receipt. That is the only receipt you get from the philly local office. If things do not work out in time, that is what you will have to use to get an interim EAD.
I finally got my 3rd EAD from them, 7 days after my old one expired. They sent me an appointment notice and I had to go to the local office and sit there for about 4 hours before my name was called and I was fingerprinted (only the index finger), photographed and was given the EAD. The guy who was dealing with the whole thing was a very funny and nice guy though. However, he had no clue regarding what was happening with my I-485 application. On the same day I also went to the support center and gave them my FP for the second time (this was in response to the 2nd FP notice I got earlier). So I am good to go for one more year now. Hopefully a decision regarding my case will be reached by the end of it. If not, I shall apply for my 4th EAD by Oct 04.
Persons who want to know about filing the EAD application with the local office, you can do it both my mail or in person. In my case I filled out the application and gave it to my lawyer since he did not charge me anything for filing my EAD. One of his paralegals filed it in person and sent the receipt to me. However, if I had to do it myself, I would have filed it in person and got the receipt from them right away. I personally think, mailing your application to the Philly local office is a bad idea. Things do not go smoothly over there and you should not be taking any unnecessary risks.