Mike,
The wave piercing bow is the end result of moving more volume down to the waterline while keeping surface area constant (or reducing it.) The Acat designs did this because once you've moved the volume down to the waterline you need to remove surface area or you will end up with a boat that is too heavy for the box rule. Other designs moved volume down to the waterline in an effort to reduce wetted surface area that generally results from loading up traditional multihull shapes. Traditional multihull shapes have always suffered from adding weight as the surface area increases quickly as compared to a traditional mononhull shape.

So the net effect of moving volume down to the waterline is a pear shape with the topsides being thinner than the waterline. Once you take this shape to the bow, your classic bow shape is upside down and becomes what is being referred to as a wave piercing bow. That description is a bit misleading because even though the bows may seem to pierce a wave, the rest of the boat doesnt actually pierce the wave and the boat if affected by the wave at some point in a way thats pretty much the same as a boat with regular bows. The designers were/are more concerned with the waterline shape/volume than the bows and the bows are really just the end result of moving the volume down to the waterline.

The side benefit (and I own a wave piercing Acat) is that you can submerge the bows and the boat wont pitchpole as easily. See the recent BMWO trimaran shots for illustration. Sailing around with submerged bows like BMWO probably isnt fast, but if this happens in a gust, or during a bear away its a nice feature to have the bows keep moving underwater with little or less drag than traditional flat top bows. The boat doesnt really pierce a wave, the wave affects the boat in basically the same way. Think about a H16 and how the bows slow dramatically when they are submerged, this is what the wave piercing bows resist/avoid.

The downside of a bow with a pointy topsides is that you lose a bunch of utility, you cant walk on it, you cant attach hardware to it easily, etc.

So when you ask the question, you really need to talk to the designer and see what he thinks, and look at how he has the volume in the ama's and what the whole picture looks like. Having ama's that dont pitchpole as easily is a good idea for a 20 ft tri and something that I would consider having.

Deciding on the bow shape should be done in concert with the rest of the hull shape and boat design and not as a separate design decision.

Bill