3.5 out of the srd. WotC hasn't gotten a dime from me since Magic of Faerun. Just the way it worked out.
I recently got Minions Complete which has 3.5 versions of the Minions monsters. I got slayer's guide to demons which says it uses 3.5 material, but that is limited to DR and listing survival in their demons, the stat blocks and stats are all 3.0, when they are close to correct. Oathbound arena and Into the Black are 3.5, although I have yet to read over ItB to verify it.
That is true, but not because new material is 3.5 rather than 3.0. I haven't found any compatability issues for the most part for a 3.5 sourcebook in a 3.0 game.
But they have survival, not wilderness lore listed! Monsters have more feats, square facing, and the constructs have more hit points. How can you possibly deal with these daunting incompatibilities?
A horrible abomination I like to call "3.39e". (Yes, it's the unstoppable hybrid.)
Got the classes, skills, feats, and magic from 3.5. Everything else (notably combat, equipment, weapons, etc) from 3.0. Monsters are a mix (use whatever is the more powerful version, and use both methods of DR).
One group I am with has gone with 3.5, and the other has stayed with 3.0. Tis interesting, to say the least, especially when the two versions' rules are mixed up.