CLASS BALANCE
Let me say first off that Death Knights are overpowered. Their dominance in PvP is just remarkable, with Death Knights populating SK-Gaming's Top 100 Arena Rankings, second only to Paladins. This is due to the fact that Death Knights have freakishly high survivability coupled with powerful offensive capability that can all be used pretty much at the same time. Patch 3.0.8 looks to toning that down a bit, hopefully enough so we'll no longer see keyboard turning clickers overpower their to 2k.

Death Knight
21/ 0/ 50 Unholy Death Knights have amazing survivability, with a lot of mitigation as well as self-healing at their disposal. The ability to put up Bone Shield, Anti-Magic Shell / Zone, and Icebound Fortitude all up at the same time, with the option to use an Improved Rune Tap at a moment's notice makes Death Knights horrible targets in an Arena. The thing is, Icebound Fortitude is intended to be a tanking ability, a baseline mitigation spell that helps Death Knight tanks come along without a shield. Patch 3.0.8 fixes Icebound Fortitude to a 20% damage reduction, down from 50%, scaling with Defense.

Anti-Magic Zone's duration has been reduced to 10 seconds, but Anti-Magic Shell's cooldown was lowered to 45. That's a pretty even change. Bone Shield's damage reduction was nerfed to 20% from the original 40%. These changes all make Death Knights somewhat less resilient, but Rune Tap remains unchanged, even improved with the buff to Glyph of Rune Tap. We'll have to wait and see just how much these mitigation changes will tone down Death Knight dominance.

A large change is the nerf to Shadow of Death, which now lasts a mere 25 seconds instead of the original 45, and was given a cooldown of 15 minutes. The length of the cooldown makes no sense whatsoever, considering that it is still within the limit of allowable spells in Arenas. The cooldown should have been short enough to be more useful or longe enough to prevent use in Arenas. We'll just see it less often in Battlegrounds, I suppose.

Rune Strike was also nerfed to be less of a Rogue killer, dealing only 150% weapon damage instead of 200%, but threat generation increased. It's still a lot of damage, though, so I don't know just how much impact that will make. 3.5k strikes that can't be dodged, blocked, or parried will still be pretty commonplace. Glyph of Death Grip was changed to be more PvP-oriented, with killing blows now refreshing the cooldown of Death Grip. This should see more application in Battlegrounds and world PvP. Finally, the most powerful Death Knight PvP glyph, the Glyph of Death and Decay, was reworked to deal 20% more damage instead of the ridiculous powerful cower effect RNG.