It's absolutely insane. My barb can lazily click his way through T4.
http://us.battle.net/d3/en/profile/Drilling-1463/hero/3811704
You see the way it works is that shard of hate poops out like 4 shock pulses every time you attack with a lightning skill. Soo when you use something like whirlwind with wind shear to make it do lightning damage it just shits out an ocean of lightning bolts in front of you.
Each one does 210% weapon damage, modified by all the +lightning damage gear you have.
Essentially, each time my barb spins he releases four 7million damage bolts, and that's not counting the actual damage from whirlwind. That's not for a full rotation either, in full 1 second of me holding down whirlwind he probably does ~48 million damage.
So basically I have a few damage sources.
WW itself doing 5mil
Shard doing 7mil
Odynson doing like 10 mil or whatever broken amount it currently does
T Gods doing 4-5 mil
Pox faulds ticking for like 2mil AND procing the 210% poison nova on my shard for an additional 2mil
Andy's doing like 2mil AND procing the 210% poison nova on my shard for an additional 2mil
The only way I really die is if I get over zealous or stop paying attention...or I am in T5 / T6 as my toughness isn't high enough for that.