My position is this: Separation of church and state does NOT appear in the Constitution or the First Amendment, and it doesn't. The Supreme Court wrongly went to Jefferson's Danbury Letter when trying to decide Reynolds vs. the United States. Once again, an activist court imposed their views on the law rather than actually using the Constitution and its Amendments for the basis of their decision.
Subsequent members of the Supreme Court have lamented this gross misinterpretation: (Source)
In 1962, Justice Potter Stewart complained that jurisprudence was not "aided by the uncritical invocation of metaphors like the 'wall of separation,' a phrase nowhere to be found in the Constitution." Addressing the issue in 1985, Chief Justice William H. Rehnquist lamented that "unfortunately the Establishment Clause has been expressly freighted with Jefferson's misleading metaphor for nearly 40 years."
Jefferson's real intent:
The unedited draft of the Danbury Baptist letter makes it clear why Jefferson drafted it: He wanted his political partisans to know that he opposed proclaiming fasts and thanksgivings, not because he was irreligious, but because he refused to continue a British practice that was an offense to republicanism. To emphasize his resolve in this matter, Jefferson inserted two phrases with a clenched-teeth, defiant ring: "wall of eternal separation between church and state" and "the duties of my station, which are merely temporal." These last words -- "merely temporal" -- revealed Jefferson's preoccupation with British practice. Temporal, a strong word meaning secular, was a British appellation for the lay members of the House of Lords, the Lords Temporal, as opposed to the ecclesiastical members, the Lords Spiritual. "Eternal separation" and "merely temporal" -- here was language as plain as Jefferson could make it to assure the Republican faithful that their "religious rights shall never be infringed by any act of mine."What does this mean? I think Jefferson was saying that he felt that the Constitution limited government, not religion.
This article on the Danbury Letter is a quite fascinating read. Check it out if you are interested in such things.
UPDATE: Later in that article is this interesting tidbit:
One of the nation's best known advocates of religious liberty, Leland had accepted an invitation to preach in the House of Representatives on Sunday, Jan. 3, and Jefferson evidently concluded that, if Leland found nothing objectionable about officiating at worship on public property, he could not be criticized for attending a service at which his friend was preaching. Consequently, "contrary to all former practice," Jefferson appeared at church services in the House on Sunday, Jan. 3, two days after recommending in his reply to the Danbury Baptists "a wall of separation between church and state"; during the remainder of his two administrations he attended these services "constantly."Emphasis added. And we are supposed to belive that Thomas Jeffferson was so dedicated to the idea that religion had no role in politics...
UPDATE 2: Sometimes in getting wrapped up in the history, I forget to address the actual issue at heart of the discussion. Fortunately, Ramesh Ponnuru does that nicely here:
“Some bloggers and tv commentators have seized on remarks by Christine O’Donnell to suggest that she is unaware that the First Amendment prohibits the establishment of religion. I don’t think that’s right. What she denies is that the First Amendment requires ‘the separation of church and state.’”Exactly. But I don't expect those folks who don't get it to ever acknowledge that she is actually making a very important argument that many Americans don't understand. Why? For the most part, our education system has robbed the citizenry of critical thinking and reading comprehension skills. This is exactly the sort of circumstances that produce a culture obsessed with American Idol and other nonsense while the nation faced decline for the bulk of my adult life.