Its great to see what some people get to build in other countries. There is no way we could do something like that in this country. Way, way to many rules and regulations. Not enough freedom.
I lived in the hills 40 miles W of PDX for 20 years. All the homes on our road were un-permitted and owner built, so yes it can be done. You need to be sure of your neighbors though. I like the earth sheltered idea, but drainage is issue #1. Also, critter infiltration, so it has to be tight.
Here is a cool little futuristic sci-fi story by the guy who designed the hexayurt:
The Unplugged - How To Live Wiki