I've only sampled a few outlets, so I can't say this definitively. However, the few electrical outlets I've sampled at the Nashville airport are not working.
I've read before at BoingBoing about Pay-per use electrical outlets at DFW.
I'm guessing (just guessing; again, I don't know, as I've only tested a few outlets) that some bean counter at BNA here pointed out "hey, we're spending $XXX on electricity every year for all those moochers in our airports charging up their laptops and cellphones while using the highly overpriced concourse Wireless they purchased and while waiting for all of their delayed planes! If we cut them off, we'll save this much money!"
Never mind that it's just one more data point in the increasingly large column I have that reads "drive whenever possible." I will definitely drive if any trip is under 6 hours, and almost certainly drive if the trip is under 8 hours. At 6 hours, you spend nearly as long waiting in airports and on the plane (about a 1-1.5 hour flight, probably) as you do driving, and you deal with all the aggravation of the War on Liquids and such, and there's a good chance you spend more time than you would have driving due to a delayed flight.
If the drive is 8 hours, I'm still very likely to drive rather than fly.
I'm wondering if I should make the cutoff 10 hours. Or, perhaps, anything that's less than a full day.