I have a new laptop and took it with me on a flight from LHR to the USA the other day. Somewhere over Greenland, I switched the laptop on, realised that I had not previously switched off the wi-fi and noticed, while searching for the ability to do so, that there were 6 other wi-fi signals on the plane.

That said, I do try to follow crew instructions. I don't think it's right to ignore them just because a plane has not crashed so far (for which, read "I'm too arrogant to obey rules made for the little people"). There is a standing instruction that all electronics should be turned off for take-off - on my last flight a person continued to play games on his Nokia mobile on the opposite aisle and a woman in front continued to read her book on a Kindle throughout taxi and take-off. This is not untypical, at least in the UA E+ section which is full of frequent flyers.