2013 SV with heat pump, very impressive performance and no troubles (first winter with Leaf). 37 degrees this morning, very little reduction of range (about 5 miles on GOM) with heater on, but the car is so well insulated and sealed that it no heat is really needed if I turn on CC 1/2 hour before leaving my garage, even for a 30-mile trip. We'll see what happens when it gets really cold next month.
Hope this adds to "anecdotal data", I really feel bad for those having trouble with heaters.
Bill P -- Washington state
2013 SV Brilliant Silver Premium package (Bose, camera)
20,400 miles, 99.02% Battery
Leased - delivered 3/11/13
9.6 Kw Itek Array on-grid 5/31/13