Maybe PUGs never went away, but I sure as hell haven't stepped foot into any since wrath...
Since I began raiding with a semi-hardcore guild at the end of wrath, I haven't felt the need to pug, really. There was plenty of normal raid content for my guild to do, and I didn't feel a pressing desire to pursue heroics (in fact, the guild was clearing a good amount of heroics as it was). There was LFR for my alts, and beyond that I didn't see a need for pugs as they caused me more stress than fun.
With Warlords, however, we saw a major slowdown in guild progress. And blizzard decided it would be fun to add yet another tier of raiding - mythic. In essence all it did was push down "normal" mode raid down a notch. That was what my guild was running. I decided to give pugs another chance when I saw the new group finder feature, which looked pretty seamless - and it was, to a point.
It works kind of like a dating site, imo. You browse around to see which groups are running the bosses you want, and what their requirements are in terms of ilvl and class/role. You apply to a few, and if you meet the criteria, they'll invite you and you're in a raid group, easy as that. No more spamming trade chat for people, no more resorting to third party services like o-queue or openraid.
I found quickly, however, that making it so easy has also made pugs much more of a brutal place to be. Back when you had to spam trade for hours to find a player, you generally put up with other players' incompetence of mistakes, up to a point. Obviously if someone was really dragging down the group you'd replace them, but otherwise you sighed and resigned yourself that someone was earning a free carry.
Not in these group finder pugs, however. You make one mistake and they might keep you around, but make two in a row, and boom, you'll find yourself removed from the group. And why not? There are 20 other DPS waiting in queue to take your place. If that one mage isn't dodging fire properly or that rogue isn't pulling his weight in dps, it's as easy as a few button clicks to kick them and have a new one with a higher ilvl to take his place in literally seconds. The only hassle is to re-summon the new members (a cinch if you have a lock) and having to deal with some nerdrage.
Even healers and tanks aren't immune - their mistakes are tolerated a bit more due to their natural scarcity in the queue system, but even then I've seen tanks kicked for not getting mechanics (completely justified as this is almost a certain wipe) and I've seen healers get kicked for low numbers.
Another facet in this is that the new raid system allows for flexible numbers - bosses hp and damage scales to raid size. So that gives even more incentive to kick players. Back in wrath you had to bring 10/25 players for a 10/25 player raid - even if one or two or five were really bad, it was better than not having anyone at all. Whereas in the new system, if you have one really bad dps, it's actually beneficial to kick them, thereby reducing the boss's hp by an amount greater than what that player was contributing.
Sometimes you get invited to a group, and before you even zone in they'll kick you for seemingly no reason. I've yet to whisper anyone to ask why, but my guess is they found a high ilvl dps in the queue. Or someone complained about tier token imbalance. Or they found a friend in the guild who's done the fight before. A thousand possible reasons.
Basically, all this amounts to a brutally competitive and cut-throat raid environment. I'm constantly on edge not not fuck up - it's either pull amazing numbers, or don't make a single mistake. That's the only way I've found to not get kicked. Even if your dps isn't amazing, if you do your job properly (interrupt, get adds, etc) and stay alive to the end, you generally keep your spot, assuming your dps wasn't dead last. Or if you balls-out embarrass everyone else with your dps, they'll hesitate to kick you even if you fuck up a couple times.
My strategy has been to play it very safe, mechanics-wise, at least on heroic modes. Generally my dps isn't anything to brag about when I'm surrounded by all the better geared people so I concentrate on not dying. As the higher dps folks start dying to mechanics towards the end, my numbers start climbing the charts as I stay alive. I pad the numbers whenever I can - going balls-out aoe with my combat spec on add-heavy fights really helps.
I'm not gonna lie, it's super stressful and there are times when I wonder if I'm actually good at the game or not. But then I realize, not many people have 9/10 bosses cleared on the first week of a new raid. But man, it's really killing my sanity...