This would be a heated debate.
If you ground your boat, You WILL increase the odds of getting hit. I do not know how this can be an argument. Electricity looks for the easiest path to ground. Now that being said, not grounding your boat does NOT mean you will not get hit. Martha Bliss has a Catalina 400 that is not grounded. She has been hit twice, though I do not think either was a direct strike.
Lightning does not have to hit your boat to take everything out. All it has to do is hit close.
To ground or not to ground is a very debated subject. Most offshore boats (Valiant, etc) ground. If you are out at sea in a storm, you are probably the highest point out there. I find most production/coastal cruisers do not ground.
If I were going offshore a bunch, I would ground my boat. You are increasing your chances of being struck, but will give the lightning a clear exit point from the boat likely reducing the possibility of serious damage. If I were going to be coastal primarily and in areas where there should be taller objects, I would not.
Another option (and this one is very debatable) is to put a charge dissipating item on top of your mast. It looks like a metal bottle brush. THere are better ones and worse ones, but in general the theory is that it diddpiates the charge build up the preminates a strike. Thus, your neighbor gets struck!!! Ha! Ha!
I did put one of these on my last boat in S Florida and I never got struck. S Florida has got to be the lightning capitol of the country. THat being said, was that because of the disspator or was it because I was just lucky???? Who knows.
PS If you do use the disspator, you are SUPPOSED to ground your stick. I could not bring myeself to do that. I preferred running to the other side of the marina, throwing a chain around the forestay of another owners boat, and tossing the other end in the water. He never could figure out why he got struck so much. I told him to try a dissipator, it might help.