Many of the chairs are unoccupied, so it seems people are taking turns waiting in line, or holding seats for people who have not yet arrived. So the actual number of people holding spaces could be 300 or even higher.
And, yes, I spotted lots of Twilight shirts, and one of the Comic-Con staff asked me if I was looking for the "Twilight line." However, I did talk to a few people while waiting in line for my badge who were at Comic-Con for Avatar. One of them could barely contain her excitement for it.
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