I'm one of the people who don't think it's at all appropriate to attempt to "swift boat" McCain as a way of striking back for what was done to Kerry. As far as I'm concerned, what was done to Kerry has nothing whatever to do with McCain, and also, if it's wrong, it's wrong, no matter who it's done to.
However, since McCain's entire campaign is about electing him president because of his record, in particular, his military record, I think that his record is fair game for scrutiny. Especially in light of the fact that he has been caught falsifying some of that record.
Personally, I'd like to know if any or all of the accidents he had that involved vehicle malfunctions were or could have been the result of carelessness or hotdogging (or lack of competence).
And I think it is entirely appropriate to examine McCain's record critically in light of what it shows us about the man. He was not a mediocre student, he was an abysmal student. He clearly wasn't considered a very good pilot (see what this article has to say about that), and he got where he is today through special treatment because of his father and grandfather.
He uses his POW status as a way of trying to deflect any critical examination of his record, but that in itself ought to raise alarms in anyone who is concerned with electing a competent and honest person for president. We shouldn't allow his having been a POW cause us to blindly accept everything he says about himself.