Can't miss rings are round, when the have a nice point at the bottom, it's getting worn out, eventually the point will turn to a gap. https://www.facebook.com/photo.php?v=10151925827726893
not sure if that's public or not, but a bit exciting.
I bent mine about 60 degrees under a dock about a year and a half ago, it looks sketch, I bent it back for just the next regatta... and the next one... and the next one... They're pretty forgiving. I also trailer mine, and have to rig and derig each time, we do about 1 or two regattas a month at various locations around california.
I played with the performance manual as well as "cat sailing in the 90's" by Rick White. I got it as a raffle prize at my second regatta and laughed at the title... but there's some fantastic information in that one with regards to speed and tuning.