So copies of P4A have been in the hands of some fighting game pros for awhile now..
Early reports are that the netcode is just as bad as KOF12's. :'(
Persona 4 Arena's netplay on Xbox360 reportedly "as bad as KOF12", matches move like underwater except for rare connections."
Hope they can fix this soon because I think that is the main reason KOF13 isn't nearly as popular as it should be.
Did a little bit more reading. Apparently it's not a problem on PS3, with good connections even on one bar. So sounds like it's something that (hopefully) can be an easy fix for 360.