I'm confident that the Supreme Court will throw this out on the presumption that the bakers liberty is being violated by the gay couples appeal to the state to enforce a contract between two non-government parties. The right to choose what relationship you enter into is more important than enforcing non-discrimination. The gay couple should understand that if they can choose who they can and can't marry, then a baker has equal right to choose who he/she does business with.
It's hypocrisy to expect the state to consent to your relationship while denying the right of others to make their own decisions.