definately under no circumstances sand blast the bottom of the boat. The damage is documented in one of David Pascoe's articles. Basically there is the danger of exposing glass strands, and wicking of water. Plus there are almost always particles of sand left in the laminate, and this causes both poor adhesion and a nidus for further blistering.
What is done is very light sanding after dewaxing before the epoxy barrier. The sanding can be just enough to scratch the surface--not really remove any material.
As for bottom paint sluffing off. There are studies being done in San Diego CA where the amount of copper in the bottom and water is being monitered--with the goal of banning copper in bottom paints. Ie the active ingredient in any bottom paint--hard or soft, does sluff off into the water. The ablative paint does have some advantages, but so does the hard type--there are several paints which definately are better--but agree check with the locals.
