We already have submissions in this contest for night lasers, night projections, but in order to truly reach a large portion of the population, promotions should take part during the day when people are their most active, and everyone is awake.
It's simple. It's fun. People love it. Everyone talks about what they saw in the sky today. People always hang around longer and wait to see what the plane is spelling out. These planes are very popular on the beach in California for advertising, they really work. I know if I saw a web address in the sky I would look it up just for fun. I'm willing to bet after a beautiful day of sky writing, online hits go up dramatically the next day.