I had never, as far as I recall, read any issues of Ron Paul's now-notorious newsletters, though those of us (as Jesse Walker noted below) who had any acquaintance with the general world of small-press right-populism (and Paul's appeal has always been to that crowd as well as to more true-blue libertarians) of the early 1990s aren't too shocked, however disappointed we are.
It is certainly worth remembering on this tense day for those who have admired Paul as a politician and as a voice in this campaign that, as his clear to anyone paying close attention to either his presidential campaign message (or his message through most of his congressional career) or to the concerns of the bulk of his current fans, that racial or anti-gay animus has zero to do with Ron Paul's campaign or its appeal. Any attempt to tar the "Ron Paul Revolution" with these old newsletters is wrongheaded and unfair. It is also worth remembering that every single other candidate is a fervent believer in policies that cause far more harm to far more innocent black people (the drug war) than old ghostwritten words that insult Martin Luther King, or insult rioters in racial terms, ever could.
This whole scandal is, for one thing, a sobering reminder to Paul fans exactly how little any of his opponents cared about him up until now, given that none of their opposition research brought any of this to serious public attention (and no, there is no reason to believe Kirchick was acting as anything other than an interested journalist looking for a sensational story).
Still, his campaign's reaction to this has been politically disastrous and given the third-rail nature of accusations of racism, Ron Paul's campaign was likely fatally wounded today, regardless of the final vote totals in New Hampshire. Paul would have done better to more thoroughly explain how it happened, how it was dealt with at the time, and address how he as a politician would deal with any matters involving race–ideally, a fervent defense of equality under the law for all. If the ghostwriter has any respect for Paul and hope for the political future of the anti-state, anti-war movement that has coalesced around him, he'd do well to step forward and take responsibility.