There's been a bit of a Brouhaha occurring due to the exploitation of the Looking for Raid tool by many of the upper crust guilds, who utilized it to gain access to their 4pc bonuses much earlier than should normally be possible. This entailed one of several methods to circumvent the "one shot at loot per boss" rule which Blizzard had been extremely clear about. Some guilds simply traded items once they had been looted. Other guilds would zone out and zone back in once everyone had passed, and still other groups had their ineligible players DC before the loot was rolled out.
This has provoked a wide range of reactions, from those who blame Blizzard for launching a flawed patch, to those who believe that those who exploited should be permanently banned from the game. Blizzard's response fell in the middle. They stripped the offenders of all items gained through the exploit, and banned them for 3-8 days, dependent upon previous behavior.
I believe that Blizzard did the right thing here. My firm belief with regards to punishment of any sort, is consistency. Without the presence of precedence and consistency, any authority will break down into tyranny.
Of course, to establish consistency, one must have precedence, and one must have measures for the offences committed. In this case, Blizzard has employed the permaban before, and just as tellingly, they have opted to have limited suspensions or even no punishments before. However, Blizzard has been, for the most part, consistent in their punishments, and from that, we can draw conclusions as to what categories Blizzard views things.
Top guilds tend to be the most visible examples of glitches, exploits, and the dreaded "creative use of game mechanics". Ensidia, in particular, has had a laundry list of offences. They got the world first Lady Vashj kill when she unexpectedly died, despawned, and respawned with something like 5% health left. No one was quite sure what happened, but Ensidia, then Nihilum, received no punishment. Later, in Ulduar, in order to beat the insane two minute timer for Hodir Hard Mode, they kited mobs from Freya's room and had several mages spellstealing a damage buff from the mobs to deal obscene damage. The buff was hotfixed to prevent it from happening again, but Ensidia received no punishment. In ICC, on their first Lich King 25 kill, they used Saronite Bombs to rebuild the platform in Phase 2, rendering the Val'kyr mechanics moot. Ensidia had their achievement and loot stripped, and were given a three day suspension.
Of course, Ensidia does not hold the monopoly on questionable actions. In Ulduar, Exodus used a Holy Pally and Warlock to cause all the Immortal Guardians of Yogg-Saron to evade glitch, allowing them to kill Yogg+0 well before any other guild. They were stripped of loot, achievements, and given a three day suspension. Paragon, in addition to the current loot controversy, caught flak for their use of eleven feral druids on their world first kill of Heroic Nefarian. At the time, the buff worked differently, it only effected the next attack you made, so Paragon stacked feral druids, who, at the time, had the highest damage attack in the game, Rip. The buff was quickly hotfixed to not affect certain abilities, and was later changed entirely in favor of a simple +damage buff for a set duration. Paragon received no penalty for Nefarian, but it can be assumed that they have for the LFR debacle, considering that they issued an apology on their guild site.
Which brings us to the events that got Blizzard to hand down the permaban. Back in Vanilla, a guild called Overrated was the most progressed Horde guild in the world. They were farming AQ40 on a regular basis, and were rightfully sick of dealing with the stupid amount of trash and annoying bosses prior to C'thun, who was the only boss that they cared about. This led to them modifying the game files to remove a wall from behind the Prophet Skeram, alloying them to skip nearly the entire instance. Everyone who was there was permabanned. The other prominent permaban was back in Ulduar, where a disgruntled GM mailed a player an item call "Martin Fury", which had an on use which killed everything in 100 yards. It was an item that was never intended to fall into the hands of players, and he used it to one shot bosses throughout the raids available at the time. He was permabanned, and presumably the GM who gave him the item was fired.
From these examples, you can see that events such as these fall into three categories. "Creative use of game mechanics," these are acts where everything works the way it says it's supposed to work, but Blizzard didn't foresee the implications before the players did. These will be fixed, either through a hotfix or a patch, but those who used the technique will not be punished. Then there are exploits. These involve altering your behavior in some way that causes aspects of the game to break, be it resetting terrain constructs, evade glitching mobs, or circumventing loot rules. Exploits will be punished with a suspension, and the removal of all loot and achievements associated with the exploit. Then there are hacks. When you use something from outside the game to modify the working of the game, such as removing a wall, or getting an unobtainable item, then you will be permabanned. Those are the precedents, and there is no reason to break them now.
I laud Blizzard for sticking to their principles on the manner, and handing down a fair punishment to those who exploited the game. The guilds in question did not hack the game, everything they did was done through the game client, therefore, it is not a hack, and not something that warrants a permaban. They have had their loot removed, and they have lost their chance at multiple world firsts. That's punishment enough.