Well, you don't know what you don't know until something opens your eyes to it. I had thought there were new features to the anti-Semitism to be found today on parts of the Western left, and probably there are. But looking (for another purpose) through the volumes on my shelves by Jean Améry, I happened upon an essay of his from 1976, entitled 'Antisemitism on the Left'. Améry wrote one of the most powerful and distressing works known to me on the experience of the Nazi camps - At the Mind's Limits. It stands alongside the writing of Primo Levi, both as a document of witness and in its philosophical acuity and depth. His essay on 'Antisemitism on the Left' can be found in the collection Radical Humanism. You start reading it and you see at once that virtually none of the themes and arguments now so familiar in the post-9/11 world is absent or unanticipated there.
We are already witnessing how political groups that regard themselves as "leftist" don't waste a word when a despot and paranoid in Uganda commits abominable murders; how they do not protest when the absolute ruler of Libya enacts laws under which adulterous women are stoned... Yet Israel - certainly no model state, but surely a polity that permits opposition... - is in leftist mythology a "reactionary" land.
[A]ntisemitism, even if it calls itself anti-Zionism, is not respectable. On the contrary, it is the indelible stain that mars the honor of civilized humanity.
Améry has other words here, as well, to which some could do worse than to give their attention:
[I]s the Left prepared to acknowledge that even if so-called formal democracy cannot attain realization so long as economic democracy does not complement it, that formal democracy must have absolute priority, since economic democracy can be built only on its foundation.
On which matter, see further here.
Apropos on contemporary anti-Semitism, I point you towards this column by Denis MacShane. (Thanks: SdeW.)