what we can do to encourage more participation in commenting.
I think the largest problem here is that people haven't had time to read all the stories they wished to with the other fests going on. I've was following six fests over the time snarry_holidays was posting, and there has been over 100 pages worth of fic to read every day from these. The shear volume has me overwhelmed. It helped in the beginning that this was only one of two fests I was following, but the backlog quickly grew.
One thing I've seen other fests do to encourage commenting is offering a prize to the most frequent commentor, or the person who left the best overall comment as voted on by participants.