Thought I would add my $0.02 since I just did 36 miles of the Mick last week on my Nishiki GT with kenda cross 1 3/8 which ride pretty skinny. This is the first thread that comes up on the trail concerning tires.

1. Loved the trail wished i could have had time to do it all, but went from Hill City to bridge C and back, I felt like I covered the highlights.
2. The tires were okay, but I spun some in loose sand going uphill and and and slid a bit going down. I spent a lot more time looking down than I would have if I had been on a mountain bike with larger tires.
3. There are some ransom washouts and loos sand but one spot in particular to lo0k out for when riding the skinny tires is right before the bridges. The bridges are bumpy and everyone slows down right before them them, so the path on both sides are pretty soft. Slow down early on the skinny tires.
4. My nishiki is the only bike I have with gearing for the hills, and I would ride the same set up again if I had the chance, the tires are not a deal breaker, just a small inconvenience.