I've just installed the new XBox dashboard and am posting this from IE on the XBox.
Seems to work really well, and I can now watch C9 videos stright on my TV without out having to download them first, though you have to use the MP4 download link to play; WMV's don't seem to work and the in page HTML5 player does not seem to have a way to go full screen; still a big improvement!
Now to go and see how well some of the Win8 features work with this.
BTW, I'me typing this on a wireless keyboard, but it only seems to work for text input, you can't scroll the page with the cursor keys, and there is no mouse support, you have to move around with the XBox controller, which actually is not that bad of an experience.
yeah new stuff coming for a lot of us.... just caution: beta has an NDA so watch what you post... don;t get banned etc...