Looking over the Perception skill, there's some things I think might need to be added/tweaked on the perception tables.
Sight
- Shouldn't the DC for "invisible" be listed here?
Sight Modifiers
- Is "shadowy illumination" areas from torches and candles gone? If not, there should be DC modifiers for those areas.
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Smell
Either the scent ability is going to need to provide a bonus to "smell" checks (+8 racial?) or there should be a limit like "creatures without the scent ability cannot detect smells with a DC higher than X (say 10 or 15)"
Also, does every Ogre stink? What if he washed up? What if that elvin courtier is wearing perfume? What's the smell DC of a sweaty human commoner? What about a flower-laden dryad? Are we going to see smell DCs for every PC/NPC race? I mean, dragons are known for having a strong smell (due to their breath weapons?) - what would be the DC to smell them?
I think it might be better to broaden the categories:
Creature possesses Musk attack/Nauseate aura (skunks, troglodytes, ghasts) - DC -15
Creature possesses a breath weapon (dragons, hell hounds, gorgons) - DC -10
Creature is rancid (ogres, bugbears) - DC -10
Creature is filthy/unkempt (orcs, goblins, kobolds) - DC -5
Creature is average clean (dwarf) - DC +0
Creature is generally clean/tidy (humans, halflings) - DC +5
Creature is impeccably clean (elves) - DC +10
Sweaty - DC -5
Perfumed - DC -5 (though you gotta wonder - what's a perfumed ogre gonna smell like? Since perfume is often used to mask smells, perhaps it should move the DC towards 10 [making hard-to-smell things easier to find, but horrid-smelling things harder to detect])
Also, the "ogre's den" tends to indicate that an area can "pick up" a smell based on its inhabitant (The dragon's lair that smells of sulfur and brimstone, a bear's den, etc.), adding -5 to the DC to detect the "lair" of a particular creature.
Finally, beyond actually smelling something, is there be a way to "identify" a smell (do you just beat the DC, or maybe beat DC by 5, coupled with a Knowledge check?). I think it might be worth making a mention that once something is perceived (by sight,sound,touch or taste) at what point you can identify the source (match DC, exceed DC by X...). I think this has just been taken for granted in the past; I think it might be worth discussing (if not in the book, at least here).