I found this review that talks about sizing, courtesy of YortXC
"Nike sold 400 pairs of Flyknit Trainers at the trials, and so being a runner, I had to pick up a pair (91st pair!). Since getting them on Saturday, I've put about 60 miles on them, and would like to share my first impressions.
I would first like to talk about the fitting process, which I had never been through with any other pair of shoes. I had to schedule a "fitting appointment" two days in advance, and be fitted with a general size (9.5...I normally wear a 10 or 10.5, but these shoes are meant to fit like a glove). On Saturday, they brought out a pair (I received red...the two colors were red and blue, and the color you would get wasn't guaranteed) and I tried them on, confirming that it was the right size. After this, they were "steamed" to a high temperature, and I had to put them back on, while still hot. The shoes then constricted down to form an exact mold of my foot, and after around an hour of walking around in them, my foot would not slip at all while in the shoe.
I've taken the shoes out for a couple of long, slower runs, and an 8 mile tempo run (training for the 5k). The shoes were fantastic. I've trained in the Zoom Elite before, and the Flyknits had more cushioning, while still maintaining a feel very similar to the Zoom Streak (marathon race shoes). On the tempo run, the shoes felt amazing, like I was running on clouds, but they weren't slowing me down.
The basic gist of the shoe is that it is a high cushion trainer that fits like a glove and is extremely lightweight.
Forgot to add: the Flyknit material feels extremely durable, and I expect the shoes to last 450-500 miles. Also, these do not have the Lunar midsole, as speculated, they are a neutral shoe."