Some people have had some issues with the XBox Live service over the last week, and this has raised a few questions. For those who can't establish a connection to the service, achievements are not in jeopardy. They are still recorded and uploaded for all to see the next time the console goes online - just without a timestamp. On the other hand, single player high scores in Arena's Melee, Meteor Storm or Gauntlet modes do require an active internet connection in order to appear on the scoreboard. The issues are intermittent and symptoms vary by person, but Microsoft is working on it. It seems like the sheer number of people playing new holiday games is likely to be the reason overloading the system, so I would expect the problems to resolve themselves naturally in a couple days.
While we're on the subject of XBox Live, here's some neato Wing Commande Arena advertisements that many people might have missed. They appeared in a variety of places throughout the XBox dashboard over the summer. The campaign highlighted the fact that Arena was Live Arcade's first 16-player game. The art is very similar, though not identical, to some of the renders featured online.