Here's some good info for many of you. I noticed that Row 22 had been showing up as completely occupied two weeks out, when I booked a PHL-SFO flight for 11/23. But I found out that was just a "block" put there by US since it was still unknown if the A321 would have the new configuration. Today -- two days before my flight -- the actual seat map was released. It's the old configuration -- and all six seats of Row 22 show up as unoccupied.

The takeaway is this: if you couldn't find your favorite A321 exit-row seat when you booked your flight and Row 22 appeared to be completely booked at the time, watch the seat maps 2-3 days before departure. At that time, Row 22 may be released in its entirety (if it's still the old configuration).