i'm sure you've seen these guys before at brookstone. i wanted one about about two years ago... but i didn't get one b/c they really don't do much except sit there. yes, they're self sustained, meaning that you don't have to do anything to it except keep it at room temperature, near light.
if you've never seen one before, the way it works is really simple. there are little shrimp in water inside a little globe, the size of a baseball. the little shrimp are like sea monkeys swimming around. algae is naturally produced, which the shrimp feeds on. the shrimp excrete waste, and a bacteria breaks it down to create CO2. the algae then takes the CO2 and sunlight to create O2...
at least, that's how i think it works. anyway, it was originally developed by NASA as an experiment for sustaining life beyond earth.
here's a larger ecosphere. it's about 66" diameter.
do you want one? is it cool enough to spend over $80 for 4 shrimp, algae, bacteria, and water?