There was a "chat" of sorts on Twitter #carchat last week, I asked multiple times about the Lease mileage limit, and what the residual would be at the end of the 36 month lease. My questions where ignored. I don't think they know yet, or they don't want to release that information yet.
I do think that if the lease residual + the initial $1999 payment and either the $349 or $379 / month payment (depending upon model you choose), doesn't have too much of a premium over outright paying cash, it is a better way to go, as you do get the $7500 Federal credit, without having to qualify for it as a Federal tax credit on your next years taxes (some people may not be eligable for several reasons), and, it puts the onus on Nissan to prove the battery pack life is good, and the car is trouble free, at least for the first 36 months, if it isn't, they will be taking a lot of Leafs back in 36 months..
Also of course it's better for your cash flow, you don't need to put out the money all at once / upfront.
If the car is fantastic, you can always buy the lease out at the end of the 36 month term, unless they try to pull an EV1, and I doubt that will happen (this time around)