Starfall is used at the school where I work as an add-on. For example, all the computers in the computer lab have a subscription and K and first graders can use it during their one hour a week in the lab. Some teachers use it in the classroom for specific purposes, such as during calendar time. No one even considers it a curriculum -- its an educational game. Even though it claims to be CC aligned, I think that it is bit silly.
That was my take on Starfall, for sure. We even had access to the subscription program (through a friend) and I found it to be little more than a game and I'm not so sure how I feel about games on the computer at that young age.
I was out tonight with a teacher/admin friend who I respect and who works closely with kids with special needs and kids living with poverty. I asked her what she thought about CC, she said, "I like it. I think it's smart."