Let's approach this from an electronics 101 perspective...
Corporate power costs aside, lets look at absolute power usage.
The AC/DC (charge car) and DC/AC (power building from car) conversion is inherently lossy which typically range from a baseline of 75% to an absolute best case scenario of up to 94%, so even with the best setup available (highly unlikely), a 6% loss in and 6% loss out would vastly overshadow a 2% gain. I'm skewing the numbers as far in thier favor as possible and still comes out to a 10% loss in power transfer alone.
Specific peak/offpeak pricing and length of time the office is powered, or the charge time of the cars is not shown, so calculation of the actual power (Kw/H) in and out is impossible due to a lack of information.
My take...yearly savings of $4800 (corporate power is about 1/10 residential power in my area, so $48000 to the average joe) doesn't jive with daily power cycling of six very expensive battery packs. Hope the warrantee covers it :)
The article doesn't specify the amount of time