At oral argument (PDF), no one mentioned the Court's decision in Citizens United. That's probably appropriate, because Hobby Lobby turns primarily on a statute (i.e., the Religious Freedom Restoration Act), not the First Amendment. Granted, that statute purported to incorporate (and modify) the Supreme Court's earlier First Amendment jurisprudence--but that wasn't what the justices seemed to focus on. But that's where the justices appeared to have some of the most difficulty: deciding what, exactly, that jurisprudence may have included. (And there is voluminous analysis across the Internet on this.)
Indeed, the only mention of Citizens United arose in a fleeting mention in Justice Ginsburg dissent:
Corporations, Justice Stevens more recently reminded, "have no consciences, no beliefs, no feelings, no thoughts, no desires." Citizens United v. Federal Election Comm'n.
For previous coverage see:
(By the way, an interesting note for timing purposes: the Tenth Circuit was the first federal appellate court to reach this issue, last June. Cert was granted, and the case was then scheduled for oral argument on March 25. This June, the Tenth Circuit is the first federal appellate court to reach the issue of the constitutionality of marriage amendments post-Windsor.)