I signed it as well, but I don't expect that Michael Moore will be promoting a veggie lifestyle. From his latest book - Dude, Where's My Country?:
"Vegetarianism is unhealthy. Humans need protein, and lots of it. Put down those sprouts and pick up a T-bone!"
He has apparently tried to be a vegetarian before and didn't like it, so I don't expect to see his view changing any time soon.