A social network for people who fly on airplanes regularly that helps
people book seats next to each other so that they can enjoy a nice
conversation rather than sitting in silence for the duration of the
flight.

(A reply referencing above idea).  Along those lines I know there is a
very lucrative black (maybe more gray) market in which people will pay
big money to find out flight plans of important decision
makers. People paid that money so they could try to buy a ticket in
the seat next to said decision maker. You've then got X hours to work
a pitch.