In the Republic, where the topic is the proper forming of character, Socrates reflects on the influence which bad myths might have, and proposes to reject them.
(This is not necessarily the call for censorship some people have read into it. Note that the Republic isn't a proposal for direct implementation of political measures; many textbooks misleadingly suggest that, by glossing its content as "Plato sketching his vision of an ideal state". But that's a grave oversimplification. The Republic is about the formation of the human psyche; it aims to explain the main excellences of character and their base in the complexities of human psychology; and it does so by demonstrating the internal processes within the psyche using a model: the model of a city-state, which makes the details more tangible in an externalized form and so helps us to discuss and explore them. This model, the sketch of an ideal state, makes up only part of the work; and though it probably lets us see some of Plato's ideas and fantasies about the political and social realm, this doesn't make it into a work of political science yet.)
One criticism he makes is that portraying the gods as vicious, unjustly violent, or deceptive is wrong: both because it doesn't adequately reflect the nature of the divine (gods who'd behave that way could not count as divine, or something higher than humans; on the contrary, they'd be even worse than humans, at least when the latter are at their best), and also because, adequate or not, it plants the wrong examples in the minds of the audience.
This criticism obviously fits the myth of Boreas we've seen Phaedrus and Socrates talk about on their way along the river in the Phaedrus. There is no way the actions of the personalized wind-god might be described as properly divine. One thing to be said, then, by the standards of the Republic, is that this story would be inappropriate for use in education. Still, Socrates in the Phaedrus avoids ethical reflection.
(Martha Nussbaum sees in this more tolerant stance a change of attitude which reflects a deeper change in Plato's thinking. She sees in the Phaedrus a shift towards higher tolerance and appreciation of emotional elements in ethics. Even if this is true, however, it would explain the acceptance of the mythical story as such, i.e. as a story which displays personalized gods and the like; it still doesn't account for the fact that the sort of behavior shown here is unacceptable. The form of the myth would be OK, but not its content.)
 More on the reception history of the Republic can be found in Julia Annas', Ancient Philosophy. A very short introduction, Oxford: Oxford University Press 2000, 24–36, and the references given there. A more detailed discussion of the inadequacy of a reading reduced to the political can be found in her Platonic Ethics: Old and New, Ithaca: Cornell University Press 1999, 72–95.
 Rep. 377d–378e
 In her The Fragility of Goodness. Luck and Ethics in Greek Tragedy and Philosophy, rev. ed., Cambridge: Cambridge University Press 2001, 225.