I had the pleasure of hearing Will Kymlicka from Queen's University speak on the topic of multiculturalism at a CIFAR event recently. Fascinating topic, and his paper on the subject is available here.
Multiculturalism in this context does not mean having a lot of immigrants in your society -- it actually references a policy about supporting cultural heritage for immigrants, as opposed to a policy of assimilation.
If you are running a business in a nation with a lot of immigrants -- and who is not, now? -- you need to consider that the mindset of your customers may not be what you think or expect it to be.
Some excellent research has been compiled and analyzed by Dr. Kymlicka, some of it showing surprising results.
Let me see if I can distill this down to the key points. [But you should read the paper, it is fascinating stuff.]
 the debate on this subject is highly ritualized, and hasn't changed much in the 35 years Canada has had a formal policy. But it needs to change now, because the situation has actually changed.
 success of such a policy is measured in terms of economic, political and social integration of immigrants. According to Dr. Kymlicka: "On all of these dimensions, there is growing evidence that immigrants to Canada fare better than most if not all other Western democracies." [WD for short]
I was actually surprised to hear this. Which shows you how often public discourse is dominated by positions, not facts.
Immigrants to Canada are more likely to become citizens, more likely to vote, more likely to run for political office than in other western democracies. There are more foreign-born citizens elected to Parliament than in any other WD, in numbers and as a percentage.
Dr. Kymlicka's conclusions are striking in their directness:
"The evidence generated by these recent studies – all of which appeared from 2006 to 2008 – provide strong evidence that multiculturalism in Canada promotes integration and citizenship, both through its individual-level effects on attitudes, self-understandings and identities, and through its society-level effects on institutions."
 There has been some apparent pulling back from multicultural policies, notably by the Dutch, but not only them. "If we look below the surface, we find that several de facto multiculturalist programs remain in place in several European countries even when their governments disavow the term – the “retreat” from multiculturalism is more rhetorical than real."
Many of the problems attributed to multiculturalism in other countries don't have strong factual support.
 There are real issues, however. Religion is the big one. Immigration in Canada was largely from Judeo-Christian traditions until relatively recently. So people brought with them values that were not at all in conflict with the core values of the population.
As you have likely noticed, this is no longer the case.
As Dr. Kymlicka points out, we can't expect the Supreme Court to adjudicate every problem -- we need to come to some kind of public consensus about what is reasonable and what isn't.
Media is another real issue. Who can forget the Danish cartoon debacle?
In Canada, we have constitutionally entrenched rights for founding groups: English, French and Aboriginal. We're going to have to figure out how multiculturalism fits in.
Racism and discrimination have not gone away. Many of our institutional responses relate to "visible minorities" but this distinction doesn't adequately describe many groups experiencing discrimination. Anti-Muslim predjudice is not the same as anti-black predjudice as anti-Aboriginal predjudice. [Yup, it's complicated.]
Finally, the economic progress of recent immigrants is far below that of previous generations of immigrants. They take longer to catch up to the mainstream.
Will Kymlicka, The Current State of Multiculturalism in Canada. Downloaded 2009.