Got the same problem (I think), once i go to 'online' my mouse starts stuttering, and when the arenas come up theyre all CLOSED and ping is "---". Soon as i quit out back to main menu mouse stutter recovers and everythings back to normal. Offline mode works fine as well. As u say, since there isnt a horde of posts over it, im assuming its just me........
Hmm should have mentioned, im a new user on the 14 day trial thingy, could it be my trial has expired after the fourth day? (Think im on fourth day... at the very maximum im on my fifth).