Nick Chambers drove a Leaf 116 miles, and got ~197Wh/mile on average. And he used A/C for much of the time. Pump up the tires and do a few aero tweaks and do lots of coasting, and maybe one could get 150-160Wh/mile?
The Prius would cost $867 to go the same 15,000 miles at 50MPG:
Nissan Leaf rated at 99 miles per gallon equivalent - Nov. 22, 2010
So, the Leaf costs about 45% less to drive that the Prius (using the $0.12/kWh and ~$2.89/gal prices that the EPA appears to be using).
So, the EPA says that the Leaf is almost 2X more efficient than the second most efficient car -- so, while we were hoping for even better; we can't be too upset with Nissan!
Edit: Here's another site that would have gotten about 97 miles on a charge:
http://www.allcarselectric.com/blog/...electric-range