Player-created content can get you banned

Player vs. Developer has a nice summary of the recent problems with City of Heroes / Villains. Players used the new mission architect system to create instances that were specifically designed to maximize xp, up to a point where YouTube had videos of people gaining 20 levels in a single mission run. In response Cryptic Studios is now wielding a heavy banhammer, banning every player who gained levels too fast from such missions, even if he wasn't involved in creating that unbalanced mission in the first place. Huge outcry of the players, and the whole positive excitement about the mission architect is turning sour rather quickly.

So much for player-created content. In a progression game player-created content will always be abused to cheat and advance faster. In a sandbox game player-created content will always be abused to create obscenity. The solution, at least according to Richard Bartle, is player-generated content: Instead of letting players freely create something, you let them generate social content. The wars in EVE are player-generated, and so is guild drama in World of Warcraft. Players don't get the power to create primary content, which is easily abused, but they do get the power to generate secondary content through player-to-player interaction.