Henry
Autoexreginated
F'n Realms and assorted homebrews. 
The fact is, (for which I have no concrete proof), the majority of players fall into two categories, which I gather from both the story hours on ENWorld, and from the conventions I have attended the the people I speak with.
First, we have DM's who have little prep time, and most of these choose a Generic Fantasy pre-done world, one that has tons of support. Faerun fits this well, and its phenomenal fan base is evidence.
Second, we have DM's with LOTS of prep time, who put much TLC into their homebrew worlds. The majority of those spice it up with modules, supplements, and the like, but it's still their world that they put much loving care into.
Greyhawk and Dragonlance fit sort of into this category, but lack of direct support has eroded the dedicated fan base that originally existed, and has moved them to the popularity of any other 3rd party published world, like Darwin's World, or Midnight, or Scarred Lands, etc.
So generally speaking, while most of us have dipped into other worlds like Planescape, Dragonlance, Dark Sun, Etc. but mostly fall back to the time-honored general fantasy, and either kit-bash a LOT, or we homebrew. It's just how work schedules and personal preferences seem to make this play out.

The fact is, (for which I have no concrete proof), the majority of players fall into two categories, which I gather from both the story hours on ENWorld, and from the conventions I have attended the the people I speak with.
First, we have DM's who have little prep time, and most of these choose a Generic Fantasy pre-done world, one that has tons of support. Faerun fits this well, and its phenomenal fan base is evidence.
Second, we have DM's with LOTS of prep time, who put much TLC into their homebrew worlds. The majority of those spice it up with modules, supplements, and the like, but it's still their world that they put much loving care into.
Greyhawk and Dragonlance fit sort of into this category, but lack of direct support has eroded the dedicated fan base that originally existed, and has moved them to the popularity of any other 3rd party published world, like Darwin's World, or Midnight, or Scarred Lands, etc.
So generally speaking, while most of us have dipped into other worlds like Planescape, Dragonlance, Dark Sun, Etc. but mostly fall back to the time-honored general fantasy, and either kit-bash a LOT, or we homebrew. It's just how work schedules and personal preferences seem to make this play out.