If every little bit really does help, then Buffalo's USB-powered heart is in the right place with this 4-port hub. Each port can be shut off individually, so if you're not using whatever USB goody you've got plugged in, it won't be sipping power in standby. We can't imagine that'll save you too much energy — unless, say, you've got a microwave plugged in or something — but if you're a rightly eco-concious consumer concerned about vampire power, then having that control is nice.
Buffalo's 4-port BSH4A02 USB hub will land in Japan in October for $40. You can probably find it from an exporter around that time, too, or keep an eye on the energy saving tech being worked on locally.