Recently, multiculturalism, and its alleged failure, have caused some minor blips in the media.
While this has not gotten much attention while the world is focused on the will he/won't he drama of Mubarak and Egypt (he did while I was writing this), I assert that this is the most important question facing liberal democracies. And a potentially fatal one at that.
Where we set the limits on the tolerance of intolerance is at the heart of a liberal democracy's raison d'être. This is inherent in the protection of the minority from the majority (read: civil rights) as well as the freedoms of speech, assembly, the press and many other aspects of life in a modern liberal democracy.
Hence, dealing with groups that reject the tenants of liberal democracy within a liberal democracy is crucial. Their intolerance is corrosive in a liberal democracy because it seeks to elevate a particular group's rights over others.
So the question boils down to: "What can a liberal democracy do to protect itself from intolerance while remaining consistent with its basic tenants?"
And I do not think that anyone knows the answer to that question right now.