This is going back some time, but I quite like the old Greyhawk Boxed set that came around the time of the Basis Boxed set. What I liked about that is that it provided a little details on most aspects of the campaign world, but allowed you to create things around it. There were adventure hooks for various regions, details on governments and creatures specific to each region. No too much fluff, but well distributed. I don't think a lot of people will agree with me on this, so it's probably mute in the light of your initial question, but I'd like to see the campaign setting governed by its fluff content, but that the crunch is inserted next to the fluff that its relevant to.
So, if you've got a specific race or prestige class relevant to a certain region, place it there, rather than in a chapter devoted to races or prestige classes. The danger is that people will tend to look at all the new crunch goodness, but forget about all the fluff. In a region by region presentation, at least the crunchy bits are distributed by region and if you're only playing in a specific region, then all the information you want about the region is in one place. I wished they done FR along these lines, but alas they didn't. These days everybody uses the crunch bits with little regard for the fluff that surrounds it.
Like I said earlier, you're not likely to follow this suggestion, but in a campaign setting where relevant, stick the fluff and crunch in the same section and provide separate sections for generic areas. Doesn't work in a lot of cases, but if you want people to get a feel for the campaign setting, I like this idea. You can always split out the crunch into separate pdf at a later stage.
Pinotage
So, if you've got a specific race or prestige class relevant to a certain region, place it there, rather than in a chapter devoted to races or prestige classes. The danger is that people will tend to look at all the new crunch goodness, but forget about all the fluff. In a region by region presentation, at least the crunchy bits are distributed by region and if you're only playing in a specific region, then all the information you want about the region is in one place. I wished they done FR along these lines, but alas they didn't. These days everybody uses the crunch bits with little regard for the fluff that surrounds it.
Like I said earlier, you're not likely to follow this suggestion, but in a campaign setting where relevant, stick the fluff and crunch in the same section and provide separate sections for generic areas. Doesn't work in a lot of cases, but if you want people to get a feel for the campaign setting, I like this idea. You can always split out the crunch into separate pdf at a later stage.
Pinotage