Cathy Young makes some excellent points in this article about where to draw the line between criticism of Israel and anti-Semitism.

…ultimately, motives matter less than consequences. ”Traditional” anti-Semitism, too, often involved motives other than simple hostility toward Jews as Jews - including anticapitalism, since the Jews were seen as the epitome of the money-grubbing bourgeoisie. For whatever reason, extremist anti-Israeli rhetoric today has become, all too often, a vehicle for the kind of Jew-bashing that one might have hoped was extinct in the civilized world.