Overbreadth and vagueness in the federal anti-child-porn law?

The Supreme Court has taken U.S. v. Williams, a case about the constitutionality of a child pornography law:

The [11th Circuit] court panel found the pandering provision of the PROTECT Act of 2003 was overbroad and impermissibly vague, saying that it criminalizes the speech of someone who touts material as child pornography when in fact it is clean or nonexistent.

In the appeals court's view, the pandering provision could apply to an e-mail entitled "Good pics of kids in bed" sent by a grandparent, with innocent pictures attached of grandchildren in pajamas.

Michael Williams, who got the advantage of this finding, sent sexually explicit photographs to an undercover agent (after initially exchanging non-pornographic photos of children).