Good news, everyone! The exceedingly laggy network play pervasive in the Xbox 360 version of Persona 4 Arena has been corrected in record time. The corrective patch is currently live and players will be prompted to update the game as soon as they load P4A up on a Live-enabled Xbox.
Joystiq's preliminary testing indicates that the issue has indeed been solved, as all matches played synchronized quickly and were virtually indistinguishable from the game's offline framerate and performance. Unfortunately, this also means that we can no longer blame our devastating losses on performance issues.