> I remember seeing somewhere that someone (specific, ain't I?) did this for
> a seat and they said that it was uncomfortable. I don't remember why, but
> they said that a less custom-fit seat was more comfortable for long
> periods.

It has to do with allowing you to move. A true custom molded to your butt seat holds you locked in one position only, which your body does not like. You can't shift your weight around or move joints a bit and such. So you cannot stay with it as long. However, for a short period of time, your control of the boat would probably be enhanced by the custom seat, if the boat fit as well.

Fwiw, I've got the wood slat seat built to the plans CLC has for the MillCreek, and I've found it to be darn comfortable. I can stay on it for hours on end without much squirming and groaning on my part. It's designed a bit like a mini Adirondac chair.