If you think of Stoneskin as straight mitigation all on its own, then no, it definitely does not work well and it's almost never worth it. However, pair it with the constant health ticks of Healing Stream on a tank that's blocking everything he isn't dodging or parrying and you can sometimes squeeze some use out of it.
I dunno. I still agree, Raglu, it just does not work well at all. I'd love to see it changed to reduce a set percent of melee damage, but that wouldn't improve it much on trash and would make it way OP on raid bosses.