I think that it should also be mentioned that many airports or FBOs handling executive aviation have, in the interest of granting their customers more privacy (from the press more than spotters), taken steps to hinder the possibilities of taking pictures close to the terminal. Many of those travelling on private jets don't particularly want to be seen and photographed getting on or off. Many of the large FBOs in the USA now have high walls around their ramp areas just for that reason. Photographing these aircraft away from the ramp is generally never a problem.