[MUD-Dev2] [DESIGN] Player-generated content

[cruise]

One of the common problems seems to be generating enough content for all
the players you'll (hopefully) have without too much repetative
grind-style gameplay.

Procedurally generated content is one option, and one I'm working on
currently, but what are everyone's thoughts on player-content?

Assuming a reasonably "standard" MMOG, with various quests that provide
achievements or rewards, how can you ensure player-provided quests
follow the difficulty/reward curve well? Is it even worth doing? What
other forms of player-generated content is possible to support in-game?
Any experience with such systems?