Yesterday on a stop-over at Dallas/Fort-Worth airport, I spotted these $2-per-use electrical outlets aimed at business travellers who wanted to get some electricity for their laptops. I found non-paying outlets throughout the airport, but wasn't sure if security would try to shut me down if I plugged into them (I was on the run and didn't get to take out my computer and check).
Last year, I had a ridiculous experience in Luton airport outside London, where a security guy told me that my laptop creates a "fire hazard," and couldn't stay plugged in. I asked for a direct quote I could publish and attribute to him, and he balked, saying he wasn't authorized to speak for the airport. I pointed out that there was a Dixon's electronics shop in the terminal full of things that were plugged into the mains and mentioned that I'd bought my power-adapter from a Dixon's just like it in Heathrow the week before. Then I pointed out that the business-lounge (which overlooked the main terminal) was full of people visibly plugged into the same electrical system. Finally he relented — and the airport didn't burst into flame. Talk about a business-traveler-hostile airport, though.
DFW is a hub for people flying cross-country, but it's not the only one. Free electricity and a laptop-friendly atmosphere are a good reason to choose to fly through Chicago's O'Hare instead of Dallas — though Dallas does have a killer BBQ restaurant that beats the food court in Chicago hands-down.
Update: Aaron sez, "Technology Evangelist just posted a couple days ago that Minneapolis/Saint Paul International started charging $3 for 30 minutes of juice."
Update 2: Andrew sez, "The Port Authority of NY and NJ provides power poles at Kennedy airport for free.