I'm not saying this lightly, the Poser node system never fails to impress and neither does the skill by some of the people here, I wish I could grasp it so well.

Looking at this shader reminds me of a "snow system" that was posted on another forum somewhere.  It was incredibly lifelike because it basically covered a scene with snow so that the snow really built-up in open areas and less so where things are partly covered, just like in real life.  Looking at it closely, you could see that in order to pull-off a shader like that, you would need a way to give the effect of buildup within the shader.

Why am I saying this?

Looking at this foam shader it's doing just that, it's like the foam is floating on the water, yet the water is what it should be, clear, or in other words, like a buildup of layers where the top is not effected by the underneath.  After seeing this foam shader, can't help thinking the snow thing would be possible as well.

Anyway, perhaps snow is something you might tackle once you perfected this, but either way