Pretty much never, except when shooting with my photography homies.

The fellow next to me had three - count 'em three - Nikons set up on tripods. We chatted a bit but quite honestly I had no idea what he was up to as he hopped between them the entire time. It really was quite the scene, with groups of friends as well as people who apparently just happen to run into each other repeatedly at these iconic locations. Sunrise tends to be less crowded but I've still found myself having to work around others in the pre-dawn darkness...
John