Just my two cents on Griselbrand, cross-posted from an idiotic foray into MTGSalvation a few weeks ago:
I've been using Griselbrand since he was spoiled, though not in the main deck. I've yet to lose a game when I Returned him, and I've yet to Dredge a single card using his ability. Drawing seven is enough. His power isn't in the life gain, nor the extra Dredge for his ability. His power is in putting life gain, Dredge, and by far the most important, the ability to draw SB cards post-board.
His lifegain wins against any Aggro without Plow. And if they can't immediately access a Plow post-Therapy, it's still irrelevant. So that's one slot in your SB(say, Ancestor's Chosen). His ability to Dredge is a second slot(say, Sphinx). Then you have his ability to draw cards. First, to draw to your cards that affect the board, like Moat or Jitte. And everyone is running a set of Chain or Claim that GB can draw you into easily. That's another DR target slot he replaces(say, Terastodon). Against Combo he can actually draw you into Therapies so that you can cast them before flashing them back. This Sunday I therapied a Doomsday player 5 times on turn two. It's common to have a land open to do so, and if you have an LED, you can even get three black mana in response to the draw, which you can even cast a Thug or the like afterwards. Or just drop the land you drew off GB That's another slot(say, Iona, or Hypnotist). Lastly, he can draw you into Firestorm. Which can not only burn out all of their creatures if you have a full grip after drawing with Griselbrand, it can also take out your opponent. And even without Griselbrand, Firestorm is worth is for the currently rare Aggro/Tribal deck, and against Hate Bears like Thalia and Ooze. Firestorm is actually ridiculous against RUG right now as well, since it kills their biggest threat to Dredge(Delver), discards through countermagic, and plays around Crypt, which most play now over Surgical since they have eschewed Snapcaster. That's another slot(say, Elesh Norn), which should easily free up your SB to add said Firestorms.
Griselbrand is in most situations, individually worse than all of the Dread Return targets that I referred to. The benefit of Griselbrand is the extra slots you get in having a target that can perform all of the needed actions. Flayer is a loss of 2-3 slots maindeck at a minimum. And does nothing without a second Dread Return unless you also pass the turn. And most decks are running one Flayer, and no target to facilitate getting to him. This is to say nothing of the additional slots you gain in your SB by condensing your DR package into two cards(I run two Griselbrand in the side). Especially when you consider that you will still need to bring in whatever anti-hate you normally need regardless of your DR target. Griselbrand also only needs to wait a half turn to gain life against anything but straight Burn. Otherwise, he at the very least will blank an attack step. His vunerability is easily mitigated by discard, and just off of the top of my head, RUG, Dredge, Dream Halls, Sneak and Show, U/R Delver, Burn, Storm, and pretty much all Tribal and Stompy decks have no effective way to deal with him. RUG getting their Delver blocked, you gaining 7, and them having to still double burn him out doesn't really count.
*Currently, I am trying the 1 GB, 1 FKZ configuration in anticipation of the uptick in Sneak and Show, and Storm. It's probably not needed. But I hate to pass the turn against SnT since they can topdeck a lot of outs if they have already landed Sneak Attack.