The only airline I've been on that had in-flight WiFi is AirTran, and their legroom is so tight that I could not imagine trying to use a laptop in their cabin. I even had a free coupon to use it on a flight and had to pass. If the person in front reclines forget about using anything larger than a cellphone.
reply to ElJay I've used GoGo a few times and it's great. Cost is not an issue since my company pays for a Wi-Fi roaming service. Makes the time fly by and I can do email and get other useful work done.
But I'll only do it when I get upgraded to First Class, which as a very frequent flier happens most, but not all, of the time. In coach there just ain't enough room. I don't really see how most airlines could expect to sell this to coach customers. I was on a short-haul Air France flight last week that had decent room (I could even cross my legs!), but that's the exception rather than the rule.