>two-button toilets: yes, that is the technical term (not really. i think the technical term is dual-flush). fairly simple math: small button is for small flushes, big button is for bigger ones. but, having grown up in extravagant america, it took me a while to figure this out. just think how much water they save (in case you don't want to do it in your head: about 2/3 of what is used by a regular toilet). and they're everywhere.
>carbon taxes: they're not in place yet, but sarkozy has said that over the next year taxes on the emission of co2 will be put in place. let's hope.
>timed hall/stairwell lights: because people forget to turn them off, and then polar bears die.
>density: paris is small. as such, it has an incredibly efficient public transport system, the possibility of walking places, and less far for cars to travel as they go on their merry, planet-killing way.
>vélib: bicycles, for almost free, everywhere. i personally hate riding bikes. but as a general practice of the parisian population, i have to give it a (green) thumbs up.
everyone know those online tests you can take to calculate your ecological footprint? if not, go take one:
the reason i mention this is that if you click on the u.s. as your residence, your footprint is automatically much larger than if you click on europe but all other entries remain the same. and now you know why!
p.s. i've left things out. if anyone wants to share more, please do.