My DH and I built a three room cabin last summer out of earth bags. Because we were building in Montana, we opted to use lava rock to fill the bags for added insulation. We were running out of time by October, so covered them in a mud/straw mix to see us through the winter. It worked well, but started to fall off when the Spring rains came (too much sand in the mix). This past week we started putting papercrete on the domes. It's been a wonderful project.
If we were to do it again, we would get the UV protected bags - the intense MT sun really does a number on them, and they were hard to keep covered while we were working (pesky wind up here). We have some pics on our blog:
http://halcyontimes.wordpress.com.
Jen