And left visible damage, would you just drive away like nothing happened?
I just don't understand why the world is full of A-holes anymore!   
 Last year someone hit my swim platform and left a mark.  Yesterday I pulled the boat and while cleaning the water line I found the boot stripe damaged and a chunk taken out of the gel coat.   

  There were also a few other superficial marks that look like they will rub out.  But as I looked at the side of my boat I can tell it was hit quite a few times.  There are too many marks to be just one incident.
I've NEVER hit another boat.  But if I did, especially if I left visible damage, I would man up and leave a note apologizing and offering to pay the repair.  I'm so pissed that I'm thinking about not keeping it in a slip next year.  At the very least I'm going to have a talk with the marina management and see if they can move me next to someone more responsible and that gives a shit!  There seemed to be a different boat in the slip next to me every month all summer.  If it had been the same boat I'd have a talk with the guy.
I've seen people hang bumpers down the side of their boats and even met a guy who would tie a cheap Kmart inflatable on the side of his boat when he wasn't there to keep this kind of stuff from happening.  I always kind of chuckled at them but now I'm thinking I may have to join them.  What the hell else can I do?
Ok rant over.  I just had to vent.