Dark Meditation can save your ass if you got 4-5 stacks of Ether Drain and Demonic Payment. So it can be useful if you have problems with mana outage and dying or rendered useless due to mana issues.
Example of a usable tribuild:
http://goo.gl/keUemB
That build could be used at Entity (not that minus hate matters at Entity) or Archfiend. Max magic damage from feats, a bit hate reduction, mana feats and soul resonance from Havoc. Flame Body and instant Planar Shift to counter Bombardment or Brutal Force. Fires of Gehenna as main attack to stack Incinerates and gain mana from Consume Flames.