SONY has rolled out JB 4.3 bug fixing update with build no:12.1.A.1.201 on 2/FEB/2014
The update is around 750 MB if you update via PC Companion and 9.4 MB via OTA.
SONY stated that the update will bring:
Enhanced user experience
Improved battery life
Software performance improvements
Now I am getting around 300 MB of free RAM instead of 150 MB
The Music Beat Light Effect is working Perfectly now.
I did not find any lag on 2 hrs of continuous usage.
Camera on the lock screen disappeared
I am not able add widgets on the lock screen
When the phone is switched off and charging is done, the battery icon doesn't appear after some time.
If You find any lags or problem then please lets us know. Post your comments regarding the same.