I think it's interesting the Michael's backstory is the first one without a real hidden secret. He was basically a good dad who had his son taken from him. Othe than lying that he was Walt's guardian instead of telling him that Brian simply didn't want him - he has no secret like we have seen from Jack, Sawyer, Kate, Sayid, Locke, Boone, Shannon, Sun, Charlie and Claire. I think Michael is there only because of Walt and s "secret" he may have - whether he knows the secret or not.
Also, intersting point that has nothing to do with the storyline. Do you think the Hurley character is going to have to start dropping some serious weight in order to stay true to form to being stranded on an island. They have hardly any food and I think at his size we would start seeing some serious weight loss ala Tom Hanks in Cast Away - just a thought.