Grimbold Blackhammer:
Sorry if this is a duplicate thread but I didn’t see another. We’re usually so low on troops, I’m wondering if raising up undead units is worth it over Metal/Hashut/Death. Has anyone tried it yet?
Billy Ocean:
Yup yup. Tried it couple of times. My strategy was not exactly to beef up the army in terms of numbers - after all, most of the spells do not really give you enough points worth to place solid combat units on the table (with the exception of boosted Harbinger, which can be hard to get off).
Instead, I have been using the lore to raise redirectors at critical points, either to facilitate another round of shooting on a nasty unit, or to prevent counter charges. To this end, the lore has been working very well. I had particular success raising ethereals (spirit hosts and cairn wraiths) in front of small punchy units that don’t have the ranks to cause the spirits to crumble through static CR. Kept a unit of 4 demis out of a whole game by raising spirits in front of them in this way.
The downside of course, is that there have been situations where I sorely missed my usual lore of metal. Have missed Searing Doom badly, and my unit of 30 great weapon IG kind of underperforms without enchanted blades / glittering robe to buff them up.
My overall assessment: a nice gimmick, but won’t replace metal or death in my tournament lists. The 12" restriction on summoned units is really the killer - my pop-up redirector tactic would be much more viable if I had greater range with it and could manipulate the movement phase from the outset. As is, I have to wait until my opponent’s whole army is almost at grips with me before beginning those shenanigans.
I have played against Nagash now, and in his hands, Lore of Undeath is really something to behold. I doubt other armies without his bonuses will find it useful enough to replace their usual lore. BUT I do 100% recommend everyone experiment with it a little, I’ve had loads of fun, and its something new for us to do, so why not? 
Geist:
All I can say is:
Unless your playing VC its a waste of time on your behalf. If you are playing a game with nagash on the field drop arty on his head. He wont survive for long and sure as hell can not hide out anywhere.