... still the players, but the devs can rank right up there too.
A big issue with player created content is that there will always be opportunists, designing content that makes farming for XP easy. The Mission Architect (MA) system had a number of things taken out before launch to try to reduce this exploitation potential somewhat, but there were always going to be issues.
Farm missions (also called meow missions; I'm assuming that catgirls are somehow to blame) were (and are) pretty prevalent, which I've covered before. Using Rikti Communication Officers - a mob type that gave above average XP because it could summon mulitple Rikti mobs through a portal - was a common way: load up the mission with them, send the players in, mop up and reap the rewards. Also used were hiccups in the way XP is delivered to sidekicked team mates, so that a level 40 might get the XP rewards that should be given to a lvl 50. And so on.
Matt Miller (aka Positron) came out on Tuesday to announce that players found abusing the MA system could face the loss of access to the MA system, the removal of badges and even the banning of accounts. And: it would be retroactive. This set off the biggest threadnaught in recent CoH/V memory, with enough players threatening to quit and go to Champions Online that you'd think Jack Emmert had done a deal with his old studio for some extra publicity. The core of complaints was the uncertainty over what the term 'abuse' meant. There was anger, there were tears, there was high drama.
This drama was mainly driven by the fact that their were a lot of players who were overtly and covertly worried that they'd been exploiting the system. Some were at least honest enough to admit they had probably at least come close - they'd done farm missions en masse to get the badges, to get the XP, to earn in-game currency / rewards, all on a huge scale over multiple characters. Ultimately this is because all that separates a farming team and a non-farming team is forward momentum: a farming team will repeatedly hit one mission / arc because it provides maximum rewards, a non-farming team will change missions / arcs and head towards the mission objectives slightly quicker. Their actual play style - lay waste to all before them - is pretty similar.
On Friday Positron decided enough was enough with the threadnaught and released a clarification: only the worst of the worst abusers would be banned. The forum community is slightly calmer as a result, but plenty are still looking for a fight or to score points off a dev.
Player created content is always going to be a risky thing - by giving players enough rope, a developer can end up hanging themselves. Positron dealt with it the wrong way - he was too blunt, which often got his predecessor Emmert in trouble - and ultimately angered a lot of players. As a developer, you can't just put tools for the player to create content and stand back, unless you want a train wreck. Along with some sensible restrictions on the toolset, developers have to also have to put a big "DO NOT DO THIS" list next to the tools so that players don't have have any excuse for creating content that could be considered abusive. This list shouldn't be in patch notes, or email, or on forums - it has to be with the tools. Heck, make it something that has to be clicked through every time a player publishes a mission.
Otherwise you risk alienating your player base from a feature a lot of people have come to try out.