I've been using PreCheck with AA at LAX mostly (in MIA once, in JFK once) and once with AS from SEA (by entering my GE number on AS website) with 100% success rate except for a single flight which was the last one in an International itinerary.

I had entered my GE number on continental.com way back and forgot about it but at JFK last week at UA security in T7 when my mobile BP was scanned a LLL popped up - I think that indicates that my number is successfully in my UA profile.

I know where PreCheck could be for UA at SFO - at T3 elite security three out of four belts now lead up to a nudascope, but one still only has a metal detector. I wonder if that's the one that it will be at (really soon, I hope!)