I fall into the OTHER camp because it has varied heavily from campaign to campaign.
I ran a comedy campaign where it was literally "Anything Goes". Since it wasn't at all serious, I didn't care about races, classes, prestige classes or much of anything else. If someone found something and wanted to use it, all they had to make sure of was that I had a copy of the pertinent material. Ta da!
I had another campaign where I had a LOT of restrictions. Only human. Only these classes. Only a very limited group of PrCs. The following spells are Out or In. You are given magic items, but you can't buy them. The material came from WotC and SSS, nowhere else.
My current campaign uses WotC, Green Ronin, a bit of SSS, a bit of Mongoose, and a couple ideas the group came up with on their own.
In general I am fairly open to material, but it all depends on the specific campaign and everything to be added must be GM approved ahead of time. Oh, and what's sauce for the goose is sauce for the gander, meaning if PCs get it, NPCs get it, too.