My stamping experience
I think you already know that the USCIS office is in the south side. The address is 3000 Sidney Street and you should be able to find directions easily on mapquest.
Infopass appointment is not required if you are planning to go before Nov 1st. But I encourage you to make one. The security will not let you into the building before 15 minutes of your appointment. They will ask you for a Govt issued photo id (DL) to let you into the building.
The office is on the second floor. The entire process will take you less than 20 min from then on. Show your infopass confirmation and you will be asked to wait until an officer is assigned to your case. At the officer's booth, you will have to produce
1. Courtesy Copy of approval
2. Two front view passport photos (kinko's, sears, kmart will do this)
3. All EADs and APs
4. Passport with I-94
They will take your signature and right hand index fingerprint in two places. The lady said we can expect the actual cards in about 6 months time. That is all. Then your PP will be stamped.
The whole process was very smooth and there is hardly any wait time.
We also took time today to visit the SSA office on Penn avenue to request correction to the Social Security card. This correction will give you a new card (same number) but without the "Valid for work only with INS approval" and/or "Not valid for employment" text.
Hope this helps. Let me know if you have any other questions I can answer.