Bryan Caplan lists a few reasons to be sceptical  about the Card & Krueger study that purportedly shows no unemployment effect from minimum wages. His overall point is that, beyond traditional labour economics, there is quite a lot of empirical evidence to show that minimum wages create unemployment. My favourite point:
4. The literature on Keynesian macroeconomics. If you're even mildly Keynesian, you know that downward nominal wage rigidity occasionally leads to lots of involuntary unemployment. If, like most Keynesians, you think that your view is backed by overwhelming empirical evidence, I have a challenge for you: Explain why market-driven downward nominal wage rigidity leads to unemployment without implying that a government-imposed minimum wage leads to unemployment. The challenge is tough because the whole point of the minimum wage is to intensify what Keynesians correctly see as the fundamental cause of unemployment: The failure of nominal wages to fall until the market clears.
I wrote about the labour economics research into minimum wages in a paper on the Living Wage last year . Even if you think minimum wages are a good thing, the levelof ambiguity around the consequences of raising the minimum wage should give you pause for thought. There are no straightforward solutions to low pay, but if there are ways of increasing the net income of the poor that don't risk putting people on the margin out of work, aren't these the ones that we should focus on?