Difficulties for habitability around white and brown dwarfs

Habitable Planets Around White and Brown Dwarfs: The Perils of a Cooling Primary
http://arxiv.org/abs/1211.6467

The problem is these stars start off luminous and cool down, which means any habitable planet would have been very strongly heated in its early stage, possibly triggering a runaway greenhouse and water loss.

I'm not particularly optimistic about white dwarfs which put out large amounts of high-energy radiation in their early lifetime (though you might be able to do interesting things with second-generation planets if you are very lucky), but brown dwarfs may be a somewhat better bet.