Picked up a very interesting paper from a link at New Scientist magazine about the possibility of long term habitable zones around white dwarfs, and the possibility of habitable, water bearing Earth-like planets being in orbit about these stars.
http://arxiv.org/abs/1103.2791
Seems that the chances look quite good, depending on how the planets got there (be it after WD formation or through migration of the original system's planets). In order to detect transits by Earth sized planets around WD's, long term surveys of upto a minimum of 1000 WD's within 100pc of the Earth would have to be carried out. Only scopes of 1m aperture would be needed to undertake the work. The major advantage of these surveys is that the Earth-like planets would be a large fraction of the size of the star, so the transit depth would be quite pronounced, making their detection much easier than for transits of ordinary stars.
Seems like something that would be worth doing. Might make a good topic for PhD candidates in the field
