I don't know why people are afraid they'll nerf them. The amount of whining on the forums about it is ridiculous. They're designed specifically to be challenging content for those that want it. They're not required, they're not the only way someone who doesn't raid can get gear (like heroic 5 mans). LFR, nerfs to 10 man raiding, and nerfs to the difficulty of 5 man heroics are there to help the casual players get gear with PuGs. The fact that challenge modes aren't puggable via the dungeon finder alone speaks volumes.