I basically copied Barcode's inquiries word for word from the Hiding = Invisible? thread and sent them off to the Sage. Here is his response:
Sounds good to me.
Dear Mr. Williams
Does a hidden character count as "invisible" with regards to the "Attacker Invisible" entry on table 88 of the PHB, thereby giving a +2 to attack and denying the target its dex bonus to AC?
Usually, yes.
If not, does the hidden character deny the target its dex bonus to AC implicitly, perhaps without the +2 modifier?
No Dex bonus for the defender.
If not, is a hidden character at least considered 100% concealed for defensive purposes?
Not seen=100% concealed, unless the attacker has blindsight.
Skip Williams
RPG R&D
Sounds good to me.