I was going to just write something about Ensidia being banned, but I think that their banning is also part of a larger question. Where exactly is the line between exploit and strategy?
It's a complicated question, one which is up to the game developer staff to decide, which unfortunately leaves it open to the judgement of one or a small group of people and therefore is subject to opinion.
So what exactly is an exploit?
Let's start from the top. The following in an obvious exploit where there is no room for misinterperetation, and while a permanent ban may have been extreme I don't really disagree with that decision.
This is a quote from one of Overrated's members in response to their banning for an AQ40 exploit:
Let me explain. We are the only US Horde guild that clears Naxx [the most challenging area of the game], been like that for a few weeks. People found that the pre-C'thun trash was so painful, that they decided to install some stupid thing that deletes walls or something, and you can just run there after Skeram [the first boss]. I know, we had it coming, blah blah whatever, we know we deserve it...I'm sure they'll try and get it rescinded because it's kind of a steep punishment with no recourse or whatever.
Another good example is Exodus' world first kill of Yogg-Sargon (0 Keepers). The guild leader of Exodus explained it as such:
The bug is when someone is left inside the brain room of Yogg-Saron, they can still get aggro on the adds that spawn in phase 3. That means if you have someone getting healing aggro in the brain room, they will get aggro on the adds, which cause them to evade in place and allows for all of your raids dps to be focused on Yogg.
The above is still clearly an exploit as it allows you to effectively despawn mobs that are integral to the challenge of the encounter, and it is something has to be done intentionally (as there is really no reason for anyone to be inside the brain room in phase 3) but at the same time - no external programs were used. No game code was changed. So while this one still lands well within the boundaries of an exploit, we're starting to cross over into "clever use of game mechanics" territory.
Further down the exploit ladder we come to EverQuest and the Statue of Rallos Zek. This was a mob that was once thought unkillable due to the sheer amount of damage that it would dish out on the tanks. This extreme damage was a part of the encounter and ironically, it was Tigole's EverQuest guild (Legacy of Steel) that first killed it - by tanking it with other NPC giants who were Mind Controlled by the guild's Enchanters.
We're now well into the area of strategy, instead of exploit. While a major part of the encounter is still being intentionally negated, players are using the abilities available to them in order to complete an encounter, sure there is some outside of the box thinking going on, but nothing they are doing is interfering with the encounters normal mechanics, they are simply dealing with it in an unintended way.
At the bottom of our exploit ladder, landing safely into something that even the most aggresive banners (Blizzard) do not consider an exploit, you have something like the three drake rush style of completing Sarthation. The idea is to go in with 1 tank, 1 healer, and 8 DPS. Use Heroism/Bloodlust and throw everything you can at Sartharion while someone kites the first of the three drakes away, and you kill her before the second one joins the fight.
This effectively allows you to ignore a very large part of the encounter, but at no time are you preventing the encounter from following it's script, and more importantly, you're not doing anything you wouldn't normally do.
So what's the take away? How does this help us understand what an exploit is in comparison to the oft-used phrase clever use of game mechanics, and does it shed any light on who is actually right in Ensidia's recent banning?
While finding these four examples, I read over many stories of guild bannings both large and small, and the common factor in deciding whether or not something is an exploit seems to be whether or not you can do what you did outside of the encounter in question, and whether or not you are actively preventing the script of an encounter to follow it's natural course.
Enchanters in EverQuest could always charm mobs, and use them to tank. It was a generally accepted strategy for a handful of fights or for experience grinding. The Statue of Rallos Zek "exploit" ultimately caused the developers to change how charmed mobs act game-wide, but no one was banned for it as the players were just doing what they normally did it just so happened that this made the encounter in question much easier. Additionally, at no point was anyone interfering with the mobs ability to do what it would have done anyways. It didn't act any differently while fighting giants than it would a player.
Similarly in the three drake rush, players aren't doing anything they wouldn't normally do. Kiting instead of tanking is a fully valid tactic for many encounters, and having a lot of DPS is not an exploit in any situation. The three drake script is not being interfered with in any way.
So now let's look at Ensidia.
They were banned for killing the Lich King due to the following:
I'll let MMO-Champion's Boubouille explain rather than reword it myself.
First, it seems that the bug was caused by a single rogue (always blame it on the rogues!) who used Saronite Bombs throughout the fight. Apparently the siege damage caused by the bombs bugged the encounter's mechanics and respawned the platform destroyed by the Lich King during the encounter.
It results in the fight being fairly easier because you end up with more room to move and more importantly, you do not have to care about Valkyrs taking away your raid members anymore. (They will just land on the rebuilt platform when they fall down)
The problem with the Saronite Bombs is simple, a lot of rogues have been using them for the past months (and it's been documented on ElitistJerks for quite some time now) and a lot of high-end rogues who like to maximize their DPS just consider it part of their normal DPS rotation.
Initially, this looks like a no brainer - Ensidia has proven through combat logs from previous fights (and really, for most high end rogues this is common knowledge) that Saronite Bombs are used all the time. The Rogue was not doing anything that he wouldn't normally do in any other situation - so it's not an exploit, right? Unfortunately, they are interfering with the script of the encounter. So it seems that this is sort of a grey area, left up to a question of intent, which is why it is getting so much attention.
My personal opinion, for what it's worth, is that Ensidia did not intend to abuse this bug. They had no way of knowing that Saronite bombs were causing the platform to respawn, and so they went on to complete the bugged encounter assuming that it was simply broken in some way they could not control.
There is no way for Blizzard to prove malicious intent, and they should have had enough understanding and knowledge of their own game, and the way people play it to know how likely it was that this was simply an accident on Ensidia's part.
When Blizzard realized what had happened, they should have removed their achievements and titles, fixed the encounter, apologized and allowed them to try again. Banning them was really just a slap in the face, and I'm not really surprised that a handful of them are quitting.
In the end it seems that while you can safely determine what is and is not an exploit based on a handful of criteria, there is still a grey area somewhere in the middle that can only be decided by determining the intent of the accused, and unfortunately that is something that may never be known.