Patch 5.0.4 brought a ton of interesting changes, including a change to PVP gear that removed Resilience as a stat, introducing "PVP Resilience" and "PVP Power". If you're not into PVP, this probably seems like a rather unimportant change that won't affect you.
However, what many people don't realize is that when Blizzard changed the current tier of PVP gear, they also - for some reason - changed PVP gear so that they are perfectly acceptable options for PVE content as well!
"Wasted stats" = no more!
One of the two biggest strikes against using PVP gear in PVE has been one simple fact - normal PVE gear comes with two PVE secondary stats (such as Crit, Spirit, Hit, etc.) while PVP gear only had one PVE stat and Resilience, which was useless in PVE. Therefore it was almost always a severe handicap to use PVP gear and "lose" an entire secondary stat.
However! The PVP armor that you can currently buy for honor now comes with two secondary PVE stats, making this gear absolutely fine for PVE content! (They also have PVP Power and PVP Resilience, but these are irrelevant for this discussion.)
And the real kicker? The PVP gear is ilvl 390, which means its primary stats (Intellect/Strength/Agility) AND secondary stats will be higher than any 378 PVE piece (such as Firelands or Dragon Soul 5-man drops), AND higher than 384 PVE pieces (such as LFR Dragon Soul pieces).
If you're wearing pieces from Firelands, End Time, Well of Eternity or Hour of Twilight, the 390 PVP pieces WILL be better. It's not even worth delving into comparisons, it's not even close.
Things are a little fuzzier when it comes to 384 LFR pieces, specifically gem sockets and set bonuses. Generally, the PVP gear will have just as many sockets as the 378 pieces (or more), but some of the 384 LFR pieces will have an extra socket. However, don't be fooled by that alone - remember that having an extra socket but 30-40 less base Intellect (or other primary stat) is basically the same thing, except it'll cost you an extra gem just to equal out.
As for set bonuses? Critics will be quick to point out that using PVP gear means you'll lose out on the PVE tier 13 set bonuses. And they're not wrong. But don't just ignore the PVP set bonuses! You have to ask yourself - what is more valuable? Your 2/4-piece set bonus from using 384 LFR gear? Or higher base Intellect/Strength/Agility, higher secondary stats, and the PVP 4-piece bonus of +160 Intellect/Strength/Agility? Not to mention the varying utility bonuses that also come with a PVP 4-piece set. Granted, some of them are useless in PVE, but some are still okay, such as increased movement speed after Dispersion for Shadow Priests. And some are pretty good!
Need some hard facts? Okay. How about Holy Paladin? Let's compare a full 5-piece LFR set with the 5-piece PVP set. For this comparison, all sockets filled with +50 Brilliant Queen's Garnets and using Burning Shadowspirit meta. Enchants ignored because they would be identical.
Holy Paladin LFR (384) 5-piece
2247 Intellect (+1693 from gear, +554 from gems)
2315 secondary stats
Reduced mana costs after Avenging Wrath
+5% increased Holy Radiance healing
Holy Paladin PVP (390) 5-piece
3065 Stamina (+167 increase)
2427 Intellect (1863 from gear, 404 from gems, 160 from 4pc bonus) (+180 increase)
2548 secondary stats (+233 increase)
+160 Intellect (already added in)
+400 PVP Resilience
+10% increased Holy Shock damage and healing
Just think how many gems/enchants 180 extra intellect and 233 extra secondary stats are. And that Holy Shock heal bonus isn't garbage, either.
Persuading the haters
Now, I mentioned two major strikes against using PVP gear in PVE content, stats being the first. The second is the stigma. I guarantee many people will get a sour look on their face at the very NOTION of using PVP gear in PVE content. Granted, previously they had good reason. But now? When PVP gear sports two full secondary stats like any PVE piece? This attitude no longer makes sense. There is absolutely nothing wrong with the 390 PVP gear, and in fact, it's as good as - if not better - than anything short of regular 397 Dragon Soul drops.
As of 5.0.4, if you automatically dismiss PVP gear as being unsuitable for PVE content, you are a) out of touch, b) WRONG.
Now, this PVP situation isn't a miracle solution. The gear is useless for tanks, since PVP gear doesn't come with Block, Parry or Dodge. And the weapons/shields/off-hands still only have one secondary stat (and are ilvl 384), so they're still not worth using in PVE. (Generally. There are exceptions but this is beyond the scope of this post.)
But the armor is great. And while many people aren't intent on pre-raid gearing up for Dragon Soul this late in the expansion, it's a nice way to replace those 1-2 pieces you haven't been able to get LFR drops for, improve your Armory profile for upcoming Mists guild applications, or even just to kit out your offspec before the expansion hits.
Personally, Fabulor's Retribution set is garbage, so I've been collecting a Ret PVP set to have an easier time leveling once he hits Pandaria. And I picked up the Holy PVP ring to replace my 378 one, since I can't win the Ring of the Riven from LFR-Hagara to save my life.
Now, it does appear that Mists PVP gear will continue to have two secondary stats as well as PVP stats. Take for example, the Dreadful Gladiator's Ornamented Headcover, which has a familiar-looking 2pc bonus, and a 4pc bonus that would still be pretty nice in PVE. That being said, I'm not sure how they will match up against equivalent PVE pieces. Something to keep in mind in the future, in any case!
PS: I do NOT recommend trading in/farming JP to exchange for Honor Points to buy the 390 PVP gear, because you're better off spending those JP on the ACTUAL PVE purchasable pieces, which are ilvl 397, and therefore superior.