However, we don't have to worry about that due to a little bit of leftover Cataclysm balance. Back when death knights were still the only "active tanks," we pointed out that it felt a little bit unfair to be the only tanks that needed hit and expertise just to survive. Blizzard, as a temporary fix, adjusted Death Strike so that Blood Shield always triggered, even if the Death Strike itself missed. This adjustment, as of this writing, has not gone away in Mists.
In short then, because Blood Shield always triggers, we don't need to worry about Death Strike connecting as much, and there's no real reason to get hit and expertise.
Does this mean hit and expertise are useless for a blood death knight tank? Not at all. You can still use those stats for extra threat and DPS. In addition, It can be pretty frustrating to lose a disease application due to a miss, so sometimes that alone is reason to invest in some extra hit rating.
We don't know yet if this little quirk is intentional, an oversight, or something Blizzard plans to fix in the future. Certainly, Blizzard removed some other temporary blood tanking fixes from the Cataclysm era such as the 30 second cooldown on Outbreak. It could be that means this feature is semi-permanent. It could also be removing it caused some bugs and they're looking for a better way to remove it in a future patch. Whatever the reason, hit and expertise are currently not mandatory or integral to a good blood gearing strategy. The choice on whether to use them comes down to extra threat and DPS vs. extra survivability, and you have to decide for yourself what is better for your situation.
What level 75 talent should I take?
The level 75 talents, which deal with rune regeneration methods, have been perhaps the biggest sources of controversy and disagreements in the death knight community since its inception. This will probably continue on as long as they exist in one form or another.
If you're looking for a quick and dirty answer on which talent to choose, rune tetris is still generally the way to go. For all specs, most sims do suggest you'll generally get the biggest DPS boost by taking Runic Empowerment and gaming the proc so that your preferred rune always regenerates. Blood Tap sims slightly higher sometimes, especially unholy, but only if you use that button at just the right moment.
That said, all options still have their perks. Blood Tap is the only option that gets procs from Death Coils used to heal or shield, which means you can keep your blood charges up in more cases. In addition, having an emergency rune means you can save it apply it when you need it most, which can be a bonus especially for tanks who want an emergency heal available whenever. Finally, Runic Corruption just plain takes the guesswork out and allows you to go all out with one less mechanic to worry about, and if you're not on the bleeding edge of content, that may be all you need.
I just dinged level 90. What should I do?
My first recommendation would be the run the Arena of Annihilation scenario. A good, solid blue weapon is the best investment you can make as a DPS death knight, and even provides a nice threat boost for a tank death knight. Get that ilevel 450 blue weapon from the scenario's quest. If you're an archaeologist, you may also want to try to dig up the Spear of Xuen, a pandaren archaeology rare. While it is an agility weapon, the base DPS means it is still worth using until you pick up a heroic dungeon weapon or better. Just be sure to replace it with a strength weapon as soon as you can, that's all.
In addition, I would recommend running more scenarios. As small group undertakings with less risk than a heroic dungeon, they're a great place to hone your skills without as much fear of failure. If you want to tank, see if you can keep threat and stay alive tanking a scenario. Perfect your damage rotation and learn to time your proc usage in a scenario. As a bonus, the cache you get at the end could contain some heroic gear.
Daily quests are your next step. Unfortunately, it's not as clear which faction to grind first in Mists as it has been in the past. Check out our reputation gear guide for some hints here. Sometimes, it may be worth it just to grind the faction that looks coolest, or split your time between factions until you have everyone to honored or revered and thus have a decent outlay of gear to choose from. Of course, if you're a blacksmith, the Klaxxi have some recipes you'll want to get ASAP.
You can also start to run heroic dungeons. Heroic dungeons are the new normal dungeons of level 85, and need only 440 item level to run. That may not be something you have immediately upon dinging level 90, but if you can buy an item or two of valor gear with the valor rewards from dailies or scenarios, you'll be there in no time.
In addition, you can also look into buying crafted gear from Blacksmiths (or crafting it if you are a blacksmith). The Masterwork Spiritblade Decimator or a set of Masterwork Phantasmal Hammers will probably set you back a pretty penny, but both will be as good as any weapon drop from heroics. If you're looking for a cheaper option, look into buying the Contender's Revenant set. At item level 450, a full set should help you get just to dungeon queue level. It's also PvP gear, so if you prefer PvP, it'll start you off. Don't worry too much about using it in PvE, though. Now that PvP power and resilience take no item budget, this gear does just fine as a stopgap. As a bonus, the Contender's Revenant set takes only 69 Ghost Iron Bars for a full set, so it should be relatively easy to get, especially if you are already a blacksmith or miner.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.