Focus Sash Darkrai is really good actually. People forget that, as a lead, its sleeping and killing something is a distinct possibility against a variety of teams. Most notably against stall and balanced teams that lack powerful priority and/or very fast Pokemon.
I'm sure it is no foreign situation to lose one's Choice Scarf Palkia to a +2 Darkrai who held on by the tip of its sash; then, to find that there exists no faster Pokemon on one's team and you have to let something take a hit from a +2 Darkrai.
Obviously Focus Sash fails in certain situations where Life Orb would succeed, like against Lum Tyranitar and Tank Ho-Oh.