Chess Theory

Standard chess is, beyond any reasonable doubt, a draw with best play, i.e. a theoretical draw.  That means, from a theory perspective, that all positions in all "playable" openings are of exactly equal evaluation (0.00 in chess computer terminology, "=" in opening book terminology).  So what are all the other evaluations appearing in openings books and on computer chess programs?  From a theory perspective, those are all just probabilistic estimates as to a position's true theoretic value, which can only be one of ("white wins", "draw", "black wins"), or in computer terminology ("+#", 0.00, "-#"), or in opening book terminology ("+-", "=", "-+").

The interesting and wide-open questions are then:

1. Where exactly is the line between "playable" and "unplayable" in the opening?  Or, how big is the gray area between "playable" and "unplayable", can it be reduced, and if so how and how far?
2. What is the function from computer evaluation value to numeric probability?  Or is this an apples-to-oranges comparison because of the inherent uncertainty in the value (dependent as it is on how much, how deeply, and which parts of the move tree the computer has searched, let alone the computer's underlying base (0-depth) evaluation function)?