/Patch 4.0.1 (12-Oct-2010): Redesigned. No longer scales spell power with spirit or increases damage done by Mind Flay or Mind Blast to targets with Shadow Word: Pain.
Patch 3.2.2 (2009-09-22): Now grants spell power equal to 4/8/12/16/20% of spirit, up from 2/4/6/8/10%.