For my take on it, for what I and my group do, we have a sort of social contract, but not spelled out on any document as some do that I've heard in past threads. Our rule is this:
---The DM has final authority in all rules disputes.
---If a dispute is not resolved in a coupleo of minutes, then the DM makes a ruling and sticks with it for the duration of this session.
---If a player would have decided that he would not have done a given action, knowing the outcome, then he is allowed to amend that action and do something else.
---Between game sessions, the actual rule is looked up, and the DM discusses it. If he's okay with the by-the-book version, then it is used. If he is dead-set against the book version after all discussion, then he still has final call over it. The players have the option to ret-con any character decisions based on the final ruling.
---The player has the option when it's his turn to DM to do the exact same thing.
---Everybody in the group has the option to not play. That's obvious enough to not even need a ruling. If people are tired enough with the campaign at hand, we can opt to play a different game with a different DM, if desired.
Now, an excellent question was brought up by Storm Raven and Celebrim's discussion; what DO you expect when you're playing by the "D&D rules"?
I expect only the least: The iconic six attributes, a range of classes and races to choose from, feats, skills, and equipment for my character, and the use of Hit Points, Armor Class, and Saves. That's pretty much it. I'd like to know any house rules ahead of time, but I'm also open enough to allow for them on-the-fly. I do this because no person is perfect, and no one can know all rules at all times.
However, if I DO know a rule is changed, as Celebrim noted, then that rule should not change between now and the time I take advantage of it. If so, then I have the right to accept it, or find another game. I have never met a DM that was so inconsistent that this occurred, though.
That's my take on it, anyway. For me, life is too short to be so concerned with the rules that I will stop someone's fun over them. It's my call to use or walk, and that's the extent of my powers. I can't make someone be a good DM.