I used to work on the London Eye, and often couples would rent out an entire pod (along with a waiter to serve champagne and chocolate), usually with the intention of proposing at the top. It never happened to me, thank god, but I heard horror stories of the proposal being turned down, followed by an excruciating 15-minute descent in silence, with some poor temp worker offering consolation truffles.
Moral of the story is always have a quick escape route planned, I guess.