I've tried and Blood spec. It's viable but subject to occasional burst like any other spec, really.

I respecced Unholy to compare and WOW what a difference. Stealthy is right, the Ebon Plaguebringer talent is just too powerful to ignore. Fights are shorter conserving mana and also making it less likely for bursts to occur.

My group's DPS went up from 1400-1500 to 1600-1800. I actually rarely had to pop Heroism during fights and could save it for the tough fights.

So, the Blood spec experiment is officially over.