Also, this piece had some useful background:

Apostasy is a grave sin in Islam, and according to classical Shariah, it warrants a punishment of execution. But Islamic laws, including those governing the treatment of apostates, were developed as early as the eighth century against a vastly different political and social backdrop.
Progressive Muslim scholars argue that the meaning of those laws has been lost over time: When the laws were created, they say, apostasy was seen as the equivalent of treason. “To be a Muslim was to live in an Islamic state or empire, so the presumption was you were not only becoming the enemy of God but the enemy of the empire,” said John L. Esposito, a professor of religion and international affairs at Georgetown University.
Muslim jurists who support the execution of apostates often point to a hadith — a tradition attributed to the Prophet Muhammad in the seventh century — in which he is recorded as saying that a person who changes religions should be killed.
But while the Koran mentions ridda, it never calls for the execution of apostates. There is no record of the prophet killing an apostate himself. And executions of apostates have been rare in Islamic history.
“The common argument is that it clearly contradicts the Koran, which says there should not be compulsion in religion,” said Khaled Abou El Fadl, an Islamic law expert and professor at the University of California, Los Angeles.
What complicates the debate is that Islam has no central doctrinal authority, no Vatican to issue an ultimate decree. And while Shariah is the product of human interpretation, it is also seen as divine law, which prompts many Muslims to argue against change.
Still, only a handful of apostasy executions are known to have occurred in Muslim-majority countries in recent decades.
An official of the United States Commission on International Religious Freedom, an advisory body created by Congress, said he knew of only four such cases: one in Sudan in 1985; two in Iran, in 1989 and 1998; and one in Saudi Arabia in 1992.
The notion that classical Islamic law calls for the execution of apostates is widely known but often ignored in predominantly Muslim countries. Most have not adopted official laws against apostasy.