I mentioned this above and Alan Sepinwall talked about it in his blog on the show, too, but I do tend to lean towards the idea that the origin/story of Don's birth were something at were used against him as a "whorechild." But it seems, upon reflection, that the very stylized, theatrical, Steinbeckian opening sequence show that Don -- as others have said -- has taken that hurt and twisted it into something that makes his parents look bad and his mother look good. Don is taking the reality and selling himself a fantasy. Not to mention the mythological aspects of being almost literally left on a doorstep in the middle of the night...in a basket, no less.
I definitely think this is something we're going to return to over the course of the season, whether it's finding out the truth behind the fantasy* or having Don's perception of things catch up to him...I'm excited to find out.
As someone who enjoys talking about reactions to the show as much as the show itself, I really liked
this blog from Newsweek about female reactions to the series and the character of Don Draper. I know a lot of people who share this opinion of Draper the character and Hamm the actor, and I also know a lot of women in their twenties who feel the same way about Elliot Stabler/Chris Meloni from SVU -- that he's a "man's man," the kind that isn't around anymore.
*As was pointed out in many commentaries/blogs, the whole London Fog thing is a great summary of the episode, and the show. London Fog is a "great name," but the reality behind it is that it was this dirty, disgusting thing. And you could very easily apply that to what we saw of Don's birth and see that there's probably a dirty truth behind it.