Odd, to me, that this topic comes up. As I rode my new bike yesterday, I was wondering how comfortable the saddle would be at longer distances. This in turn, had me wondering if it is possible for a saddle to become over time, er..., "butt-ground". ( However the words I was thinking were, "molded to my form" or conversely, could my form mold to the seat, that is, adapt to the saddle.)
My old bike had a comfy saddle, so it wasn't a concern for me.