I have now watched 2 BD movies on 2.12 firmware (The Men Who Stare At Goats and Public Enemies). "The Men Who Stare At Goats" played flawlessly under both 2.09 and 2.12.
Public Enemies was nearly unwatchable. It froze up once every 15-20 minutes, with the player making sickly "I can't read this disc properly" grinding noises for several seconds before continuing. At one point, it froze completely and I had to take out the disc and put it back in TWICE before it would play again. The first time i did this, i was greeted with a "This disc cannot be played" error. The second time, it played the movie fine (with one or two more freezes as described above). The disc was clean, though it was a used copy of the movie. I never tried this movie under previous firmware versions.
I'm becoming very tired of the weird playback issues. Most movies play fine, but you'll hit one that won't play properly. I realize this is the state of Blu-Ray on most non-Sony players, but really, this is not much of a standard if you compare it to DVDs. DVD players would really only freeze up during normal playback if the disc was very dirty or the player was defective.