I was there when it was shown and also at the closing ceremony when they talked about it. They asked us all not to take any pictures or videos. ILM threw it together just before Celebration so they would have something to show. They didn't start filming yet.
From what I remember about the trailer:
It starts out flying over a forest looking down, then it starts panning up and you see tie fighters flying and eventually a very huge death star in the sky. Then it fades to black with a black hawk down type of chaos going on over the radio.
It is going to be about stealing the death star plans. All of the jedi are gone and the rebels have to make it happen on their own, so it is a very desperate and critical time. It will have a lot of war in it hence the name Star Wars.
They also showed some concept art which I took a picture of in the closing ceremony. If its not already out there, I will post it when I get a chance.
I thought it looked good, except the death star was way too big in the sky to be confused with a small moon in A New Hope. The only way it could be that big is if it was in a super low orbit.