I've seen this discussed on blogs before, and I just recently was chatting about it via twitter with one of my blogger friends. Many Black people find Mad Men unappealing because of the lack of Black people on the show, and that those who have been shown included the maid, an elevator operator, and a Playboy Bunny.
I LOVE Mad Men. It's one of my favorite shows.I think it needs to be understood that the show's creators are trying to stay true to the times, and at the time, Black women were maids. Now, this isn't to say that there weren't any Black people doing anything worthwhile in society at that time because there definitely were, it was during the Civil Rights Movement. BUT, those Black people are not likely to be the Black people that the Roger Sterlings and Don Drapers of the world ran into.
I don't think Black people are badly represented or underrepresented on the show because I can fathom that following the characters we follow, we are seeing Black people as they would have seen them. Encountering them with the frequency that they would have encountered them.
It does seem from this season's premiere (where there was an unprecented number of Black people shown lol) that they may be tip toeing a bit more into the Civil Rights Movement. I'm interested in seeing how things will go, and if they will hire a Black secretary.