It would seem as though this technology has now come of age. I see a couple of different brands for sale at the local Best Buy. My main question is whether or not these active noise cancelling headphones are compatible with smaller portable devices like iPods and PSPs. Aside from the fact that the earcups must require more energy because they're creating more sound than earbud style headphones, the noise cancelling processing must also use some amount of juice. Do these combined factors pretty much rule out their use on small battery operated devices or are they now efficient enough not to matter?