My first response is that if the tax credit is a concern, then that person would be smart to take advantage of a Leaf lease, since the federal tax credit will be included in the Lease price (courtesy of Nissan).
But digging deeper into the issue of a Leaf purchase...
I was interested in finding the amount of federal tax that people actually pay, so here is what I found on the taxfoundation.org website...
Year 2007: Total avg tax rate 12.68%
In average terms, that means an average household with an income of $59,148 would have a tax liability of $7,500. Granted, using averages sometimes can be misleading, so look at the last two columns in the table. The top 50% of taxpayers pay an average of 14.03%, and the bottom 50% pay 2.99%.
At least the top 50% of taxpayers (and probably more) at or around the 14.03% rate should be able to get back a decent amount of the tax credit, if not all.
As far as the bottom 50%, they certainly pay less taxes. But the honest question that I have to ask, with no disrespect intended, is whether a person or family that has a lower income at the bottom of the tax tables would be able to afford a new car in the price range of the Leaf, tax credit or no tax credit?
A $32K purchase with tax and license is probably closer to $37K out the door. So even with the possibility of a tax credit or state rebate, is still a very sizable purchase for a family that makes $35K or $45K or $55K at the lower tax rates.
If the tax credit is an issue with income / tax rates, the Lease deal is the way to go.