Public proposals are lame, in my opinion. I suppose in the beginning it was a brave thing for a man to do, because he was risking rejection in front of lots of people. Now it just seems like a cheap trick to get her to say something she'll regret, or to make up for the guy's inability to be genuinely romantic.
You don't have to make a big show of it to tell someone you love them. You don't have to hire a plane to write your proposal in the sky, or propose in public, or do any of the other stupid things guys are into doing now. It's really simple. When the moment is right, you just get down on one knee and say what's in your heart. The setting doesn't even have to be staged. The location of the proposal should not affect her answer unless she didn't love you in the first place.
A few weeks ago when I was attending a youth meeting of the Assembly of God, I witnessed something that made me disappointed in men as a gender. They had this woman get up on the stage without an explanation, and sit there in a chair for like 10 minutes while a slide show played with pictures of them as a couple. Most of them were just multiple pictures of them in the same place, and some of them are badly developed. Then the guy walks in with flowers in his hand. Now remember this place is full of about 600 religious fanatic teenagers screaming at the top of their lungs.
The guy talked to her from way across the room with a microphone, and when she tried to walk over to him he yelled at her to stay on the stage. It turns out they had only known each other for maybe a couple months, and that most of that was done by e-mails because he lives in Texas. So he flies all the way from Texas to propose to her, and decides to do it in the middle of the Assembly of God.
She did say yes, I just feel like he could've done better. I would've been humiliated in that kind of situation.
In conclusion... I think public proposals are tacky.