Call me the romance scrooge but I find public proposals a bit naff. I think most of the time its attention seeking rather than actually romantic.

DH proposed to me after we went on a hot air balloon ride. I was pretty positive he was going to and I was really pleased that he waited until it was just he and I together rather than in the rather tightly packed balloon basket full of meaningless strangers. He knew I'd always wanted to ride in a hot air balloon so combined it with a special adventure

I think that with public proposals the poor 'proposee' is like a deer in headlights - what if they want to say No?