If you haven't taken a look at the 2006 CES Keynote (streamed video here), featuring Microsoft everything, it's a rather interesting look at technology. Most notably, at 1:25:55 into the stream (yes, one hour and 25 minutes), during the Xbox 360 portion of the film, Peter Moore (Corporate Vice President) lets out that Street Fighter II will be hitting Xbox Live Arcade by March. w00t!
There's also a lot of detail in the presentation about Media Center and 360 integration, as well as the announcement of an external HD-DVD drive attachment. Yes, they denied releasing upgraded versions later on, but didn't say anything about an add-on. Since I've let my 360 take over DVD-playing duties to save some space, I find the idea compelling, depending on cost.
I'm more excited about Street Fighter II though. I hope it's also online-multiplay enabled, I'd like to be able to take on my brother again without needing to fly him out here.
I looked around before I posted this, but while I was out having lunch it looks like 1UP posted some more information, which looks like it came from an official announcement of some sort. Not only is it online multiplay enabled, it has a spectator mode with voice chat for an arcade experience. I bet Spanner would like this one ;)