BEARS: Marrowgar is very simple to tank. Whether you're main- or off-tanking him, you'll need to stack up on your fellow tanks to mitigate damage from his Saber Lash, and keep him turned away from the raid. Stand there. Build threat. Build more threat. Swig your nightly cocoa. Check the stock reports. Because targets of Saber Lash can't be targeted for Bone Spike Graveyard, that's all you need to worry about for Marrowgar's "phase one."
Regrettably, you do need to move in this fight for his "phase 2," which makes him considerably less relaxing to offtank than Mother Shahraz (for whom the off-tank(s) could set themselves to auto-attack while parked on top of the main tank and AFK to make a sandwich). As he transitions to phase 2, you will see Marrowgar emote that he's beginning to spin. That's your cue to take off in order to avoid his whirlwind damage. Truth be told, getting hit by Bone Storm is not generally life-threatening on the normal version of this encounter (we saw 2K/hit damage), but you should try to avoid it anyway because its heroic brother is considerably more potent. Going cat for this phase for the speed boost (assuming you have Feral Swiftness, and you do have Feral Swiftness, right?) can be helpful, but if Marrowgar has headed your way and you've backed yourself into a corner, hit Barkskin and shift to bear.
If it's toward the end of the phase and he's going to become tankable soon anyway, you might as well just stay there to pick him up, because he wipes aggro at the end of phase 2 and is also untauntable. Make sure Feral Faerie Fire is off cooldown in the seconds before Marrowgar reverts to phase 1, and ask your hunters for a Misdirect. Continue to keep him turned away from the raid (very important while the raid repositions, so as to keep your buddies out of Saber Lash).
CATS and MOONKIN: This is not a difficult fight to DPS, although you will be required on occasion to split damage between Marrowgar and his Bone Spike Graveyard target(s). Moonkin will be occupied with this more than cats, as ranged DPS will typically be able to reach Graveyard targets faster than melee can. Melee, however, will need to be a lot more careful of Coldflame, as you will have less time to react than ranged. Strafe out of the way the moment you see it spawn. Because Marrowgar has a very large hitbox, you should be able to avoid all of it as long as you're vigilant.
If you become the target of Bone Spike Graveyard, all you can do is just sit there and wait for your fellow raiders to get you out; I got hit last night and was surprised to see that Barkskin is unusable while you're trapped there.
Phase 2 advice is roughly the same; stay out of Marrowgar's way and Barkskin preemptively if you're likely to get hit. Because Marrowgar wipes aggro after finishing Bone Storm, it's generally a good idea to time any DoT's on him to end before he resets. Because Bone Storm lasts 20 seconds, you've got time for a fresh Rip/Insect Swarm/Moonfire cycle, but not a reapplication (and cats obviously will not be refreshing any DoT's on him at any point while he's whirlwinding). Doing otherwise will give your raid a taste of the phase-transition-aggro-hell that was Leotheras. Give your tank a second or two to get solid aggro on Marrowgar after the aggro reset, and then resume your normal DPS rotation.
Of the two druid DPS specs, moonkin have a much easier time on this fight. The constant interruptions from Bone Storm are not (as you've probably already figured out) all that kind to the cat's John Madden approach.
TREES: Matt Low's article on healing the Marrowgar encounter is a great general guide. As with tanking and DPSing, this is not a really tough fight, and trees have a significant advantage in their ability to heal effectively on the move. This comes in handy on phase 2 with Marrowgar spinning every which way and most of the raid in motion. The 2K/hit damage is easily healed through by HoTs as long as people aren't parked in the middle of the whirlwind, and if you want to preempt some of this damage, spend a few seconds applying (or reapplying) Rejuvenations to melee DPS and tanks before Marrowgar goes to phase 2. These players are the most likely to be hit when he ramps up his whirlwind (and you can count on this happening if someone's not paying attention to the raid warnings), and you can easily Swiftmend someone who panics and runs in the wrong direction.
Roll HoTs on the main tank and off-tanks to keep a steady stream flowing through Saber Lash, strafe out of any incoming Coldflames, heal anyone caught in a Bone Spike Graveyard (think of it as a far less dangerous and non-chaining version of Kel'Thuzad's Frost Blast), and you're all set.
Every week, Shifting Perspectives treks across Azeroth in pursuit of truth, beauty, and insight concerning the druid class. Sometimes it finds the latter, or something good enough for government work. Whether you're a Bear, Cat, Moonkin, Tree, or stuck in caster form, we've got the skinny on druid changes in patch 3.3, a close look at the disappearance of the bear tank, and thoughts on why you should be playing the class (or why not).