My long feature on using Wi-Fi at airports--which ones, how much, and how--is online at JiWire: JiWire asked me to talk to the major airport hotspot operators and collect both a comprehensive list and write up an extensive set of information about cost, availability, and tips. There are no big surprises in the article, but I hope it will be a useful guide for anyone planning business travel.
It shouldn't have come as a surprise, but most airports in North American now have significant if not airport-wide coverage. A few large U.S. airports still lag, such as Chicago, Atlanta, and Los Angeles, but Chicago and Atlanta will shortly have comprehensive service.
More importantly, most of the airports below, say, the 25 busiest have Wi-Fi across all gates and terminals.