Southwest (25%) Not surprisingly the Sheldomar Valley and Sea Princes region is popular (I myself have worked from here the last several years). This area saw the most development in the early 2000's with Living Greyhawk and is also a favorite setting for it's heir, Greyhawk Reborn.
Northeast (4%) The north all in all is underdeveloped and very wilderness oriented which may lead to why few people make use of the barbarian lands or even places like Nyrond, Tenh and the Pale which only figure in sourcebooks like the Marklands.
Southeast (10%) This area mainly comprised of the Iron League states and the Great Kingdom should be more popular. The fact Ivid the Undying never saw publication is a travesty because the area could've been a whole series of sourcebooks in truth. I still think the popularity of Game of Thrones could bring this region new life if all the damages to the southeast were rolled back to pre-Wars era.
Baklunish West/Beyond (6%) Surprisingly more used than the northern lands, though there is scant publication on these areas. We seem to have some Baklunish land fans out there despite this and I myself of course am the steward of Ull so I always enjoy when other people produce fan work for Beyond the Flanaess be it maps or simple articles. Kudos to you folk!
Central (City of Greyhawk) (51%) Lastly is the obviously most popular region with the most printed information for DMs to use. Greyhawk and surrounding lands enjoy plenty of adventure (Temple of Elemental Evil, Maure Castle, Greyhawk Ruins, etc.) That's the beauty of Gygax's world is that his most exciting region is centrally located so you can spring board from here to all the other mentioned areas.You'd be crazy to not use this area.
That's all for now. Stay tuned for another poll soon.