It's going to be nine minutes of darkness, obviously. Dialogue, sound effeects and music will play but they'll be taken from random parts of the movie making it virtually impossible to figure out what's going on. Benedict Cumberbatch's character still won't be identified.
Okay, seriously though I am annoyed by this. I have no interest in The Hobbit, and even if I did I certainly wouldn't see it in IMAX. I guess that's why we have YouTube.