This is also a case where an unholy DK has a choice to make. Since Gnaw does some damage, you can leave it on auto-cast for a slight DPS increase, or put it on a macro to provide an emergency interrupt or to prevent a mob from being stunned in an awkward place.
The problem with squashing bugs
Of course, there is still some disappointment in the death knight community that Blizzard has made no further changes, as there is a growing sense of dread that our DPS will plummet in this patch, which has been backed up by sims. Of course, arguably every patch has doomsayers who are convinced Blizzard is neglecting their class, and sims don't always paint a completely accurate picture of the issues, but the evidence is mounting that death knights may not be coming completely out of left field on this.
One issue that may turn out to cause trouble is a recently discovered proc rate bug on trinkets. With the new RPPM indicator on the PTR UI, some death knights noted that the RPPM rate on any items with procs increased when Runic Corruption is active, including the Fabled Feather of Ji-Kun. This bug appears to be active on live as well as the test servers. The fabled feather, of course, is already a cornerstone of unholy's festerblight method of DPS, so when that feather is replaced by other trinkets, the concern that unholy's DPS may drop drastically may not be completely unfounded. It also looks like Unholy and Blood Presences' rune regeneration rates will boost RPPM as well. In short, whenever we have a trinket or other item affected by the RPPM system, that proc will happen more often based on our rune regeneration abilities. When Blizzard fixes this bug, as it seems likely they will, we may need to see unholy and blood buffs to compensate. Since frost traditionally doesn't use Runic Corruption and doesn't have rune regeneration on Frost Presence, this may not be as huge a deal for that spec, luckily.
Do proving grounds prove themselves?
Proving Grounds are also in, and a quick check suggests DKs should do alright. I personally didn't even break a sweat until about midway through Gold level on both DPS and tank proving grounds. The DPS' big problem is that one type of enemy shoots a projectile that can stun you. Luckily, said projectile is easily dodgeable, and, if it explode near an enemy, will stun the enemy instead. Using this to your advantage becomes nearly mandatory when the game introduces a hozen mob that will actively run away from you. Death Grip doesn't work on it, so you'll be forced to use Death's Advance and Chains of Ice while you try to maneuver it to a position to be stunned - or just stun it with your ghoul, if you're unholy.
The tank proving grounds are where Death Grip becomes really handy. Once you get to gold, you'll find AoEing yaungol flamecasters and AoE whirlwinding hozen mobs that rush your NPC healer, so you'll need to use Death Grip to position them away from where they can damage her.
Overall, Death Knights are lucky enough that we have a toolbox that allows us to get through the proving grounds with relative ease, although I do wish Death Grip worked for DPS. The proving grounds also show the discrepancy between ranged and melee DPS once again, as it becomes a lot easier to DPS the fleeing hozen and to avoid the stun projectiles as a ranged DPS.
What's most interesting about the Proving grounds is that they look like more of a contest than the training tool many were expecting. Your raid gear is reduced to item level 463, which is the level of a full heroic dungeon set, meaning the system essentially expects you have been doing heroic dungeons before you even tackle the proving grounds. By gold level, you're dealing primarily with raid level mechanics. In addition, there's no sort of tutorial attached to the grounds. Instead, you are pretty much left to your own devices.
This certainly isn't a deal breaker, and I'll be going for those Endless Wave achievement titles when 5.4 goes live, but this still isn't really the full teaching tool many have been asking for. Still, it may inspire a couple more death knights to try some tank waves, whereas they might have been too afraid to queue for Raid Finder or Dungeon Finder as a tank, so it may still be useful that way. It's also a good tool for getting yourself acclimated to a new spec if you switch specs after a long time or for the first time. Bronze and Silver are definitely easy enough they're still probably valuable as learning tools without being overwhelming as well. It may be that if proving grounds are popular enough in patch 5.4, we might see more low level proving grounds or proving ground-style tests for new max level players or even leveling players.
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.