From neoGaf:
We can confirm that we'll be there and I can convey my excitement about the event.
As to what we're showing/saying... here are the guidelines we've been asked to follow: 
You can confirm that Bungie will be in attendance at X10 showing off Reach 
EXAMPLE: Gearing up for X10 in San Francisco. Can’t wait to show Reach to US and int’l press and kickoff the biggest year in Xbox history! #X10Xbox
o You can share when the event is and what readers can expect to see coming out of the event
EXAMPLE: Be on the lookout on 2/11 – we’ll be showing Reach's first ViDoc to the press at X10 and it will be on Marketplace and web the following morning. #X10Xbox
There will be some stuff coming. Stay tuned.
We can expect some Reach goodies at X10!!!!!!!!!!!!!!!!!!!!!!!!!!!
And LOL at MS's guidelines and examples.
