Tried to play some SFIV on Xbox Live today, and I couldn't get into any matches at all via matchmaking (no sessions found, and nobody would join in during arcade mode). I read reports online that the following message appears on people's gamertags:
....whenever they're playing SF4 online. Rumor has it that Capcom will be releasing the game's 'Championship Mode' soon, so maybe they're testing it out?
On the other hand, because Xbox Live was down, I resorted to playing Street Fighter IV on the Playstation Network. The game is still available for online play there, surprisingly.