Gabboim: If he gave her the ring in a way that would be kiddushin, and they subsequently broke off their engagement, he would need to give her a get. She would never be able to marry a Kohen after that. Pretty serious if you ask me. But that doesn’t mean that anyone who proposed in front of a crowd would suddenly be married.
BTW, my proposal was insanely awesome, it took abt 15 minutes, on the bank of a quiet lake at sunset. It was in middle of a lightening storm, and right when I popped the question, a big bolt of lightening streaked from the sky till the lake. It started pouring abt 30 seconds later.