The biggest disadvantage IMO is weight limits. You have lots of space, but can't load them down. On a monohul, the more you can pack in, the better she sails. If you over pack a cat it drags instead of surfing. Cats are designed to surf. Also, I think the helm is awkward on cats - you can't see around them very well b/c of the height of the cabin top. Everyone else on the boat is usually forward on the deck and the helmsperson gets stuck back at the helm alone - cut off from everyone else. I love the feeling of a well-heeled sailboat cutting through the water, so I don't see it as a plus that they cats sail flat. Funnest passages I have done included a rail in the water. Last thing that comes to mind is that they have an uncomfortable walking motion in choppy sea.
LaLeLu 40' Caliber
Merritt Island, FL