I've watched a couple of episodes, and thought it was pretty good. The little boy didn't seem incredibly severe -- just classic Asperger's stuff, with whatever would make the story more interesting or palatable to the general public. I thought that they did an exceptionally good job at portraying what it is often like when parents receive the diagnosis.
I looked into the reason why "Parenthood" has an Asperger's character -- apparently one of the writers for the program has a child with Asperger's. So no matter what, even if people on this forum complain about whatever representation is portrayed in the show, the guy WRITING it has first-hand experience. It may not be other people's experience, but he is writing about Asperger's from HIS POINT OF VIEW, AND making it entertaining to keep the raitings up. Whatever everyone else may think, it's my opnion that this is nothing as positive -- get the concept of Asperger's and how it impacts families out to the public, so that more people know about the syndrome.