Like racism or sexism, anti-Semitism is pretty much in the eye of the beholder. One person might take a political position (for example, opposition to the policies of Israel towards the Palestinians) and think that it is just a political opinion while someone else might think that is actually anti-Jewish.
There are some things that seem clearly intolerant toward Jews in my opinion. For example, when Mel Gibson goes on rants about how bad the Jews are, that seems like pretty clear anti-Semitism. Similarly, the things that the Iranian president, Ahmedinejad, says about Jews and the Holocaust are clearly anti-Jewish. There are also still some country clubs that exclude Jews.
Thankfully, there is not that much (in my opinion) anti-Semitism in the United States today, but it does still exist to some extent.