Rybka 2.3.1 is not showing to be stronger than 2.3 or 2.3 LK, at least in my tests so far. More games will tell the true, but I would like to present my (entirely) subjective judgement of the 2.3.1, just to see if anybody else feels the same.

It seems to me that, watching 2.3.1 play, it just isn't the same old Rybka I used to see in all previous versions. It kind of lost the magic contained in subtle repositioning of pieces that no other engine (or human) was able to understand, at least not before little fish struck. Also, it seems to me that 2.3.1 crossed the line where it made sense to:
a) keep the bishop pair
b) ignore doubled pawns on her side
c) sacrifice a pawn or 2.
Now it looks to me that these things are done just for the sake of doing it.

Dragon Mist