Slashdot linked up this Economist article detailing some problems with the existence of "dark matter". Personally I've always thought it sounded like a kludge... "we have niggling problems with our cosmology theories that could be explained by a) problems with our cosmology theories or b) a completely different sort of matter never seen anywhere else ever before. After careful observation, we're choosing option B."

Of course, dark matter theory has made some predictions that seem to have been proven, so it's definitely not a done deal. More as we find it out!