I personally haven't witnessed anything to crazy. I drove the boats from Epcot to the resorts and then over to Hollywood. It was interesting some nights, just because Epcot tends to be the more, "adult park". Also guests are not allowed on the dock while the vessel is docking, and I have seen guests jump the ropes as I was pulling out (one with 3 pizzas in hand) trying to get on the boat. I have also pulled up to a dock where a guest had 3 tripods with cameras set up on the edge of the dock. I've asked my co-cast members so I'll keep you posted.
As far as the horns, they are required.
Approaching a dock - 2 horns.
Backing up - 3 horns.
Going forward (leaving a dock) - 1 horn.
Passing another vessel on the starboard side - 2 horns.
Passing one on the port side - 1 horn.
Going under a bridge - 1 horn.
It can seem like the vessels are continuously using the horn.