There are people who play the race card without much thought like mox said, but I think that the majority of cases are indeed ones where a person or group of people are legitimate victims of racism. Being a pasty white male, I highly doubt that I will ever be the victim, however, I do have a friend whose parents are Sri Lankian (sp?), and she has to deal with other people's ignorance occasionally, right here in Halifax. The most recent case was just a few weeks ago.
"Yesterday, a person of impeccable character made racist comments towards me. Some of the nicer things said included the fact that she hopes I die, that I'm not a real human being, and that she hopes to never see another "ugly brown face" like mine again. Heartwarming, really."
Her words, taken verbatim from her LiveJournal. Fun fact: she graduated top of our class in high school. Out of everyone I know, she has the greatest potential to quite literally change the world. In all honesty, I wouldn't be surprised if she became a world-famous leader along the same lines as Ghandi, Mother Teresa, or Martin Luther King Jr. Obviously a random person can't know this about her, but nevertheless, some people automatically make judgements about her and others based solely on something as inconsequential as skin colour. This is why I can't think of a more disgusting attitude than those of racist bigots.