my infopass went GREAT!
I got my I-551 stamp and it is valid for 1 year. The infopass officer was really nice, she had look through about 200 A-files (took her about 25-30 minutes) to find mine (apparently they are in Q to be put I'm the system) and stamped my passport.
At the end I did ask her "I have a friend who had his interview 1 month ago, got his passport stamped but has not received any updates or approval emails". She said you should make an infopass and come talk to them.
There you go, you owe me $20.