The FAQ is problematic as RAW
The FAQ is updated without announcement or fanfare, which makes it difficult to track over time. Unless one is actively involved in the Pathfinder community, this means that the rules may change without you knowing about it, and it may do so often.
Official errata is a bigger deal, which gets more attention. It also tends to come out less often. It may be missed for a time, but sooner or later people realize it’s out there.
Thus, I dislike the use of FAQ as errata. The FAQ should just be explanation of how the rules already work. Unfortunately, that’s just not the reality. Paizo has taken the FAQ as an opportunity to do “soft errata” so there’s things in the FAQ that do not match the book’s rules. Expansions, qualifications, that sort of thing.
But Paizo is far more ambiguous about this point than Wizards was, and the community often gives it far more weight than 3.5 did
This is just a fact. The FAQ is referenced often, is included in the PFSRD, and so on. The errata rules do not specify any primacy or conflict-resolution rules, as 3.5’s do. Thus, there is nothing in Pathfinder’s rules that describe what is or isn’t a rule or how to adjudicate between rules sources.
Conclusion: What RAW is for Pathfinder is debatable
There just cannot be a hard-and-fast definition. You could reject the FAQ, you could require its rulings, whatever. In general, I think people wishing to tag questions both pathfinder and rules-as-written need to spell out what definition of “RAW” they are using. If we want a default definition for the site, that would have to be taken to meta.
Barring that, I think the only appropriate way to handle this is as follows:
Actual published books are RAW. No one’s likely to dispute that.
The FAQ is ambiguous. Any discussion of the rules-as-written must consider the situation both with and without the FAQ. If the books and the FAQ match, it may not be necessary to discuss the FAQ at all, since the books definitely are RAW. As soon as there is disagreement, however, it needs to be addressed. Statements like Taking the FAQ as RAW, ... but without the FAQ, ... need to be used.
This because Paizo does not define what are and are not rules.
To be slightly meta here, there’s a key take-away here for pathfinderrules-as-written questions: the FAQ cannot be an answer’s only source. Furthermore, if the FAQ contradicts the books, the FAQ cannot be ignored, either. An answer that does either is incomplete, and not in keeping with rules-as-written. If the FAQ agrees with the books’ rules, then that answer could reference the FAQ but need not, but does need to reference the books. With disagreement, both must be considered.
Addressing the Pathfinder Society
The Pathfinder Society defines its own rules. These are distinct from the book-rules that one typically means when one speaks of the rules as written. PFS play includes houserules, banned sources, and so on. It also includes the FAQ. Within the PFS context, the official rules include the FAQ. This may not be true in non-PFS Pathfinder games, and should not be assumed, but should be discussed as an either-or if there is a contradiction.