Blu-Ray Hard On Battery Life
I guess this makes complete sense, given what I know about physics. Blue lasers were actually extremely difficult to make, and they didn't emerge until nearly a decade after red-lasers hit the market. Since the wavelength of light is inversely proportional to the energy of the photons, making blue light (which has a low wavelength) takes a lot of energy. In fact, most of the original blue lasers wouldn't last very long because they basically burned themselves out. Also, as Hesty pointed out, the computation requirements for Blu-Ray and HD-DVD are far greater than MPEG2.
Slashdot is reporting that the first-generation of laptop Blu-Ray drives are all pretty good at demolishing your laptop battery. Currently you can expect to get about half-way through a movie before your laptop sputters and dies. I imagine this is something that will slowly improve with each iteration, but not a very promising first look at the winner of the HD-DVD/Blu-Ray war.