Via Kotaku, it seems that FFXI (Final Fantasy Eleven Online) has banned, in some cases permanently, "a large number" of players from their game.  From the article,

"the company discovered an issue that allowed players to create multiple items for certain treasures and rewards in areas such as Salvage and Assault by exploiting the game system.WoW oro
This 'issue' was apparently a bug - and a bug that many players had long known about before Square Enix handled.

During an emergency maintenance on November 26, 2008, Square Enix fixed this 'issue' and discovered that players had already taken advantage of it before, in Square Enix's words, 'it was addressed.'"

This "addression", which it seems had taken a year to, well, ...address, ffxi gil not only meant the fixing of the bug but a full scale investigation entailing the viewing of, "a year's worth of logs throughout all areas of the game" which as a result meant that, "approximately 400 players were temporarily suspended based on evidence gathered," with, "Approximately 550 players who committed more serious misconduct had their accounts banned."

According to writer of the article, Brian Ashcraft, "Word has it that many of the damned and banned were long time FFXI players - perma banned, apparently."

So this brings up the question; should players be punished for anything that a games mechanics allow?  Griefing, spamming chat, bug abusing, and etc; is there a legitimate argument for developers designing something and then punishing those who abuse its flaws from within the game?  If there is such a valid argument for such enforcement, what are the limits on punishment? 

While it is easy to state that players agree to the TOS (terms of use) and EULA (end-user license agreement) when they sign up to play an online game, it isn't as simple to conclude whether this is an ethical business practice or whether this is truly fair to the client, especially those who are long time patrons.