gone: The phrase "He's been gone this month," though frequently used, is better rendered thus: "It's a month since he went." The verb "to go" does not lend itself agreeably to this treatment which is common with other verbs (as "He has been known and loved for years"), and the expression "this month," for "this past month," is somewhat too elliptical to be received with favor.
gone case: A vulgarism sometimes used to denote that the affection bestowed by one person on another of the opposite sex shows him to be serious in his intentions. It is also a vulgarism when applied to one who is in a hopeless condition, as from illness.
good should never be used for well. Do not say, "I feel pretty good" or "she plays that pretty good" when you mean that you "feel pretty well" or that "she plays fairly well."
go past: "Go" usually implies motion forward, therefore, it is pleonastic to say "go past." Say, rather, that you "go by" and not past. Nevertheless a march past is a recognized expression.
got: This word is used correctly for acquired or obtained, but is incorrectly used to denote simple possession and correctly implies effort to secure something. Sometimes it is used redundantly; as, "He has got it"; the simpler form, "He has it" is preferable. "We have got to do it," while emphatic, is less so than "we must do it."