I've had people go into one of my games, voicing no opinions as to what they'd like to see, and then have them become disinterested and/or drop the game because it wasn't what they were looking for.
While I will continue drawing up fantasy worlds at the drop of a hat and for my own pleasure, I've been inspired recently to engage in acts of collaborative world creation with prospective players. The animus for such an idea came from the Dawn of Worlds game (found here) and by the excellent Dogs in the Vineyard (found here).
To nutshell it, Dawn of Worlds is essentially a game of world creation. You get together some friends (preferably people who'll be playing in this setting), pretend to be gods for a few hours, and use a turn based point system to build a world up from a blank map outline to a thriving campaign setting. A campaign setting where the players all know the history of the world. A setting where the players themselves have an emotional investment because they built a good portion of it. Dogs mainly inspires me here by way of its "say yes or roll dice" philosophy. Don't stifle player creativity because it may not fit into your image of things. It's their game, too, after all.
A few weeks ago (sorry for the lack of updates, O my public), I introduced members of my university geek club to the idea. They chomped at the bit for an opportunity to engage in the experiment. I'll be making a series of posts recalling the results and the findings of the experiment shortly.