Here is the quick math on my 2013 Nissan Leaf, about 9 weeks / 3,790 mi into ownership...(please pardon my very non-mustachian 66mi r/t commute)
Old Vehicle = 2002 BMW 525i Wagon | 24.5mpg (SOLD privately for $4,500 this month, purchased in 01/2011 for $4,695)
Current Vehicle = 2013 Nissan Leaf SV | 4.83mi/kWh of measured consumption over all 3,790mi (Purchased certified-pre owned for $13,700 @ 0.0% APR)
Total Miles Traveled = 3,790.9mi (according to CarWings, the telematics system for the Leaf)
BMW Cost = 3,790.9mi / 24.5mpg = 154.7 gallons of fuel x $3/gal = $464.20 for fuel only ($0.12/mi)
Nissan Leaf Cost = 3,790.9mi / 4.83mi/kWh = 784.6 kWh electricity x $0.15/kWh = $117.69 ($0.03/mi)
So, over the course of the last 9 weeks, my savings rate is about $154/mo with the Leaf. This assumes that all charging is done at my home at $0.15/kWh - in reality probably 15-20% of my charging is done at free public stations. This also doesn't consider maintenance and upkeep, which was significant on the BMW even though I did most of my own work. The Leaf is effectively maintenance free (tire rotations, annual cabin air filter, bi-annual brake fluid changes - all are DIY'able) and has a warranty for the next 7yr/100k.
After 4k miles, I love the Leaf. It's enjoyable to drive, well equipped, and incredibly economical. I'm excited for quick-charge infrastructure to expand into my area (NE Ohio) so we can start making some road trips in this thing!