But with the adjustment to Gauntlets of Despair this might make for a viable combo.  Now you can use WP for an opening shot, do a bit of damage and drain then auto attack with the gauntlets causing further drain.  It might not be worth the sacrifice of 2 slots though.
I have been toying with a build along these lines.  The question I have is:
Do the Guantlets of Despair actually drain mana, or just cause the enemy DG to lose mana?
I saw another post somewhere that suggested the Guantlets do not actually drain mana (as in life-steal).  Can someone confirm?