This was my actual proposal 5 and 1/2 years ago. I was quite shocked to discover that it never made it to flickr - probably because Tina was embarressed about her hat.
I set this up on a tripod, took a couple of touristy photos then on the 3rd shot, shocked Tina with a proposal. If you look closely at her face, you will notice it is blurry from her shaking her head.
The lightning in the background is authentic. As I was shooting with a 20D, I never noticed it on the tiny LCD. It was a great surprise to see it for the first time on a bigger screen.