Nail said:The more I think about it, the more I wish there could be negative values for ability scores (for all but Con). The negative values would be for book-keeping and healing; a negative score would be treated as zero for purposes of the PC's state.
Indeed.
I think Vraille Darkfang 'Easy Math Method': add all bonuses and penalities, subtract total damage and drain, then put the whole result through a {F(x) = 0 if x < 0| F(x) = x if not x < 0} function, is the simplist and most self-consistent method. You can even argue that this does not violate the 'No negative stat' rule, since the stat F(x) is always greater than or equal to zero. It is a house rule, but I think it should be a good one.