Glyph of Swift Death might end up relatively useful for trash, grinding, or even PvP. The quicker you can move between enemies (or close the gap on fleeing or ranged enemies), the quicker you can kill them. If you have the skill to keep your Soul Reaper buff up, this glyph may have a surprising amount of power.
Glyph of the Long Winter might see some use for leveling or grinding, but in a raid or dungeon situation, you should be using Horn of Winter often enough that you won't need the hour long duration.
Glyph of the Loud Horn will come down to a question of whether you prefer the larger chunk of runic power or not. In the end, while it's not horrible, it may be too weak to justify using as a Major Glyph. Of course, we can't make a final judgement until we know just how long the cooldown's increased by.
Glyph of the Skeleton won't see any use from me, because I love my geist too much, but I'm all for more choices in minion. The questions remains though, what skeleton will you get with this glyph. Will it be one of the old classic skeletons? One of the armored skeletons? Whatever it is, it could be a fun choice for anyone who's tired of their ghoul but isn't a fan of geists.
Glyph of Festering Blood removes the need for diseases to do Blood Boil's full damage. This glyph is a little dodgy for end game use just because you should be putting up your diseases at all times for the extra damage (or threat). That said, it might be useful for emergency snap threat for tanks, or for use in conjunction with Roiling Blood, but I'm not sure it's worth spending a glyph slot for it. It may be another glyph with limited use for leveling as unholy or blood, as well.
Power in trinkets
The trinkets discussed below are just some of the trinkets currently in the PTR files right now. The basic workhorse "stats on proc or use" trinkets I'm deferring commentary on in favor of the more uniquely designed trinkets. I will say, I am a bit sad we aren't seeing any cool transformations or minion summoning like we had with Throne of Thunder, but it's still a solid tier for trinkets, power wise.
The cooldown trinket for DPS This trinket not only gives you a chance for a huge burst of strength, it reduces the cool down on a select number of abilities. For frost death knights, those abilities are Outbreak, Army of the Dead, Empower Rune Weapon, Pillar of Frost, Anti-Magic Shell, and Icebound Fortitude. For unholy death knights, those abilities are Outbreak,Army of the Dead,Empower Rune Weapon,Anti-Magic Shell,Unholy Frenzy, and Icebound Fortitude.
This trinket is looking like an early front runner for best in slot. The Army of the Dead cool down may mean you can use it twice in some boss fights, Outbreak means less wasted damage using less damaging strikes to reapply diseases, and of course, having your major personal DPS cool downs take less time means more DPS. This is the one you likely shoot for, though it will require to pay attention to your cool downs and actually use them to be effective. If you aren't using your cool downs often and well, this trinket will mostly be wasted. I will have to say, I would love to see Raise Dead added to the frost cool downs on this. It's a minor DPS cool down, but this trinket technically will make it harder to line up my ghoul and Pillar of Frost at the same time for maximum burst.
Damage amplification trinket This is a trinket that amplifies not only your haste, mastery, and healing, but your critical strike damage as well. This means it's likely to scale very well, and has the added bonus of stacking with Killing Machine for frost in a way critical strike trinkets don't. Since this adds critical strike damage instead of critical strike chance, it means a Killing Machine proc is never overwriting what could have been a natural crit, but instead just becoming more potent. If there's one downside to this trinket, it's that many highly geared DPS death knights are close to haste caps and thus may get some wasted haste here, but the critical strike damage is powerful enough on its own that this trinket will be worth it.
Cleave trinket The other unique DPS trinket this tier just adds a chance to have your damaging attacks cleave and cause area effect damage. It's unclear if all damage cleaves, or just weapon damage. If all damage cleaves, something like Blood Boil or Death and Decay could get pretty powerful, pretty fast. That said, this also means this target under-performs in single-target fights, so it's probably not going to be as good as your first two choices. Still, it might be worth keeping this in your bag for trashing or grinding mobs, and the haste makes it pretty decent for all DPS specs anyway as long as you're not already flirting with the GCD cap.
Tanking damage health drain trinket This trinket hearkens back to the old days of the early Wrath-era Blood Presence, when every hit gave you some health back. I'm going to want this trinket for my tanking set for nostalgia purposes alone, but the healing should be enough to make it more than worth it.
Area damage reduction trinket This trinket has a bit of a built-in minor Anti-Magic Shell for AoE damage in PvE only. This one will be situational depending on the boss fight, of course, but so was the Mirror from Cataclysm, and that was one trinket no serious tank could be without. This may end up being the same. It has a good chunk of dodge, which should be more useful for death knight tanks in 5.4 thanks to Riposte.
Cooldown reduction trinket for tanks Much like DPS, tanks get their own version of the cooldown reduction trinket, with some added stamina. For blood death knights, they get reductions on Outbreak, Bone Shield, Empower Rune Weapon, Vampiric Blood, Dancing Rune Weapon, Anti-Magic Shell, and Icebound Fortitude. Much like DPS, this is a trinket that should be at the top of your list. It will be even better in patch 5.4, since Dancing Rune Weapon will no longer cost runic power.
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.