Some times it's easier at the curb- they don't have management hanging over their shoulder. Doesn't apply to you, but for those flying international, checking in at the curb is not an option. I doubt that you will get away without paying the fee- soon airlines will be charging for the lavatory...
In the event that the clerk at the check in counter won't let you take a kayak, be sure to have the policy printed out to show them. Be sure that you have plenty of time before the flight leaves to politely argue your case if they won't let you take it, or if you feel that the fees are too high. If there is a long line behind you, so much the better- that puts the pressure on them to solve the problem.
If there is damage to your boat, paddle or gear, be sure to file a claim within 24 hours of picking up your bag- preferably as soon as you pick it up. I had a broken paddle upon arrival in Equador, and decided to deal with it when I got back because it was 2am and I didn't speak the language. Of course, when I got back the airline (American) claimed that I broke it while boating and wouldn't talk to me.
Here is a somewhat dated account of flying with my boat in '03: