I guess I'll throw my hat into this foray. I updated the day it was released and the only thing I was experiencing was terrible battery levels. Last night, I figured out how to do a factory reset and completed it. Since then, my battery performance seems to have returned to pre-JellyBean levels, however, I now seem to be experiencing the proximity issue as many others have opined. I never had the proximity issue before, so I'm thinking it could be JellyBean related. I just got off the phone from my 8th call today, and the screen either, would not dim when at my face, or would go black and not turn on until after the call.
EDIT: I ran the Test Menu P-Test through *#*#3424#*#* a few moments ago, and the sensor seemed to be working normally. After that I received another call and the sensor seemed to be working normally again. This is quite strange. I wonder if running the test "fixed" the problem.
EDIT 2: I have solved my problem with the proximity sensor, and it wasn't related to the P-Sensor Test. There was a some facial oil covering the sensor on my phone and once I wiped it off, it worked flawlessly. I was able to duplicate this numerous times within the last hour. It seems the oil was diffusing the light and the sensor was not getting a good reading, at least that's my assumption.