Whenever a controversy begins, typically over a remark about or involving Jews, there are quickly people who emerge to argue that the individual is question is no anti-semite. And that is likely often true as well. For example when Noah writes in Slate that John Updike is no anti-semite, that is likely the case. But then no one was arguing that indeed he was.
Anti-semitism was a word coined to describe something like a dedicated antipathy toward Jews. Anti-semitism tends to manifest itself in the extreme in obsessional behavior, conspiracy theories involving Jews and responses ranging from hatred to phobia. The milder forms of Anti-semitism result in merely social antipathy, slurs and thinly disguised hostility.
But there is a vastly larger pool of prejudices that are widely held without making one an anti-semite. When John Updike describes a character as a "Rich Jew" he is echoing back a literary prejudice regarding Jews that was widespread throughout literature. From Shakespeare to Marlowe to Dickens to Trollope to Henry Adams and O'Henry, novels, stories and plays reflected what is today described as Anti-semitic stereotypes. This is however an inaccurate description.
Most of the writers listed above, aside from perhaps Adams and Trollope, were not anti-semitic as we would understand it today. Shakespeare and Marlowe had likely never even met a Jew. They were simply dishonestly regurgitating the stereotypes they knew, without ever being able to conceive that they were doing anything wrong. It wasn't until the 19th century when Jews began to talk back to writers and some genuinely understood and changed. As was the case with Coleridge, Harriet Beecher Stowe and Mark Twain.
But overall finding writers who did not see Jews in such a light up until the middle half of the 20th century was a painfully difficult task. Those prejudices are still very much alive, as liberals have helpfully managed to conclusively demonstrate over the last decade. They were simply frowned on for a while as politically incorrect. Even before disguising them as political Anti-Zionism rather than Anti-Semitism became trendy, a distinction pioneered by the Communists who playing to a liberal crowd overseas needed to be subtle in their persecution of Jews as opposed to the Nazis who quickly shed such scruples, they always existed inside.
The distinction between Anti-semitism and that kind of vaguer prejudice is tricky. An authentic bigot might say "Jew Down" but so do plenty of people who don't hate Jews per se, but do look down on them and take the stereotypes on faith. It might be the gap between the bigot and the racist. In an age when Borat exploits anti-semitism for comedy, when progressives exploit it for activism against America and Israel and the supposedly Jewish Hollywood is one of the biggest exporters of those same stereotypes on a regular basis, the issues easily become muddled.
The very pervasiveness and the ancient history of Anti-Semitism and prejudices about Jews is what makes those stereotypes and feelings so viral finding their way into the worldviews and mindsets of both Jews and Non-Jews, into literature, film, social circles and political punditry. Circumstances like the War in Iraq for the left or the Seattle Christmas Trees for the right very quickly reveal what is beneath the otherwise civil facade.
While prejudice is not the same thing as genuine Anti-semitism, one flows into the other. The modern techniques of spin and political correctness make them difficult to separate and identify. Is Mel Gibson an actual Anti-semite or just prejudiced. The difference can be bought by an expensive damage control team.
These days everyone, even Ahmedanijad, have Jews they can trot out before the cameras to vouch for them. But then prominent Anti-semites have had Jewish friends and even Jewish spouses. Henry Ford was close friends with a local Rabbi even as he was financing the printing of The Protocols of the Elders of Zion. Hitler had fond memories of an art professor whose safe exit from Germany he took care to insure.
Nevertheless in discussing the issues it's important to try and tell the two apart. It's often the difference between sworn enemies and jerks.