When it comes to Player versus Player competition, most of the players undervalue the stats that keep you live such as Resilience and Stamina and overvalue the stats that get you more crit like crit rating, spell damage and Attack Power. It is obvious that some players still maintain the ability to damage the opponent and be able to kill them quickly enough. You will realize that you do not kill them any more if you are dead.
   In PvP, resilience accomplishes four things differently in the World of Warcraft. On the one hand, it reduces the chance you are critically hit by all attacks. For level 70 players, 39.4 resilience is a 1% decreased chance you are critically hit by any attacker and reduces the damage of all critical strikes against you by double the amount of critical strike chance reduction. So for every 39.4 resilience critical strike damage will be reduced by 2%.
On the other hand, it reduces the amount of damage you take from Damage over Time effects which effects are reduced by the same amount as the decreased critical strike chance, so 39.4 resilience will decrease DoT effects by 1% and decrease mana drain effects by the same amount it reduces critical strike damage. So 39.4 resilience will decrease mana drain effects by 2%.
As you can see, resilience is extremely powerful stats for PvP players. It decreases the chance you are hit with a critical strike and the damage from critical strikes and DoT effects.
Resilience is extremely valuable stat for all classes, 400 resilience is the accepted norm for high ranking PvP players and should be everyone's goal as they start to gear up for arenas and battlegrounds. For players just beginning to PvP 250 resilience is a good point to shoot for. Until you have reached 200-250 resilience most of your enchants and gems should revolve around stamina and resilience.
Note that resilience critical strike reduction is capped at 25% which equates to 492 resilience. You can still continue to mitigate DoT effects and critical strike damage but not critical strike chance. Right now it would be extremely difficult to reach this point without over sacrificing for stats.
In PvP, Stamina is an often undervalued stat. However it is not quite the powerhouse that resilience is but should not be overlooked. Too often I find players trying to PvP with less than 10,000 health, which generally does not go well for them.
But how to Value Stamina and Resilience versus Damage increasing Stats many classes use a rating system to balance out stats so they are comparable by a standard value. For example, Agility Equivalent Points is the system Rogues use to evaluate gear options. This system takes all stats, including resilience and stamina and updates them to a value based upon 1 agility point.
You should realize that you much still damage the enemy to beat them, so remember to keep enough damage and attackpower or plus healing to prevail in the battle. All the resilience and stamina in the world will not save you if you can kill anything!
It does not sound like much this is only incoming damage from one player. The more players you add, the more damage you will be mitigating with resilience. Think about this against a 4 DPS 5v5 team and how much 12% decrease would be, and how much easier it would be for healers to keep you alive.