donikiffmeyer McCoy

Ronie: Basically, yes. While other earth bldg techniques like cob, adobe, and rammed earth require a fairly specific ratio of clay to sand, the EB method can handle a broader range of dirt ratios due to the encapsulation with the bag itself. However, a rammed earth ratio is the ideal.
Gotta love epiphanies, eh Rob? Keep in mind that the wicking action of moisture is more deleterious than actual splash back. Keeping your plaster far enough off the ground so that water from the ground or melting snow isn't wicking into the whole wall is a good idea. It's the freeze thaw action that does the greatest damage. Even for a dome. Speaking of domes, it's a good idea to have a very rough textured plaster on a dome if you expect a lot of precipitation. A smooth plaster will cause water to sheet down the wall causing rivulets to erode it. A rough textured surface slows the water down and diverts it into many different directions.
Joshua: In regards to the thread; the junctions are sealed by the way the bags are laid and then tamped after a whole row is complete. The ramming action shoulders the bags together and forces them into a very tight seal. I've never had a problem with spaces btwn the bags...and I'm not the kind of person to say "never" or "always." And yes, the tubes are great to work with. It's faster as you don't have to stop, remove the bag from the stand, fold over the top, and lay it down and force it against the previous bag. They are more expensive however as they are not "misprints" as you stated. The tubes are how the fabric comes before the cut, sew and print process, so you would not likely find tubes as misprints. Manufacturers get them in 2000 yard lengths. You can buy them that way or sometimes they have cut off ends of a few hundred feet.

First off, bags made of polyethylene are not used. The plastic variety used is a woven polypropylene. This may seem like hair-splitting, but the carbon chain is totally different for each one. The former is not woven; it's the same stuff they offer in grocery stores to put your veggies into. It tears and breaks down quickly and since it isn't woven, it retains moisture, harbors mold, etc. All the things you don't want to happen. Polypropylene is made (primarily) from recycled plastics like soda bottles. The weave allows the dirt fill to completely dry out. Water vapor can easily transpire through it.
Any type of woven material will work for this purpose: polypro, jute (burlap), cotton, etc.
As to ronie's question, the woven bag is very strong; lots of tensile strength. The bag doesn't "break" or split apart if you are using a suitable mix in the bag that is good for ramming (tamping). I once tried to stress out a bag filled with dirt by continuously whaling on it with a 12 lb. sledge hammer. I compressed the fill in the bag to about an inch high. Although the weave was stretched incredibly tight, the bag did not fail. The only time I had bag failure was when I tried to tamp a non-compressible material into the bags - like gravel. The impact btwn my tamper and the angular gravel would cut through the weave.
As for bag longevity - Woven polypro breaks down from UV degradation. Depending on where you live, this can take anywhere from a month to 6 months. The closer to the equator, the quicker they break down. Once protected from this form of light, the bags last indefinitely. This is attested to the fact by the polypro feed/grain bags that have been buried in landfills for up to 30 years (about as long as polypro has been around) are still intact when they have been unearthed. So covering your poly bag work quickly is a good idea. If you can't get around to a plaster, then even protecting them with a tarp is better than nothing.
Burlap (jute) is just the opposite. It will eventually break down when buried due to microbal and bacterial activity. Most of the burlap we get in this country has been treated with a hydrocarbon "dip" that inhibits mold growth and the breakdown below ground. Some people have an extreme allergic reaction to the chemical treatment used on burlap (like my partner Kaki) so I don't use it regularly.
Cotton breaks down from microbal action as well, but with proper care, any of these types of woven bags will work. I use polypro mostly because it is cheaper, relatively stable and some bag manufacturers sell what they call misprinted bags at a reduced cost.

Pretty good guess, Paul. As was stated in the thread of this question, dirt has an R-value of approx. 0.25/inch, so it's not the best of insulators. Keep in mind tho that the R value can be expressed as the coefficient of heat transfer or conductivity - U value (or British Thermal Unit - what we call BTU's). This an inverse proportion of R value; that is U=1/R. So one inch of dirt with an R value of 0.25 has a U value of 4.
As was also stated later in the same thread, This ability to absorb energy and slowly re-radiate it is best utilized in an earthen wall of at least 12 inches thick. This by itself works fine in temperate climates, but where in the world do temperate climates occur? Of course there are some places like that, but most of North America is not exactly temperate. Most places have huge temperature swings seasonally. Even where I live summers are generally over 100 degrees F, while winter temps drop below zero. Certainly burying or berming the structure can create a more temperate climate as the earth's temp is relatively stable below a certain depth - once again depending where you live.
There are no hard and fast rules about how a massive building built with dirt will perform. Just like permaculture, the first rule with building design is observation over a period of time.
But I know, you're all in a hurry and need answers now. If you can't wait to watch and learn, you may want to explore ways to add a degree of insulation to your dirtbag structure and there are as many ways as there are opinions. I've done dirt mixes with 50% pumice stones added to it that gave a degree of insulation, but it decreased it's R value. Remember the inverse proportion? It works both ways.
If you want to have the best of both, R and U values, you can wrap your EB building with an insulative layer of your choice. We explore some options in Earthbag Building, but there are many more that could be (and probably have been) tried. Our only limitation is our imaginations.
This was a long-winded answer to a very short, succinct question. I'll try to be less wordy in the future, but no promises. 

Hi all you budding dirtbag enthusiasts! Rob asked me to jump in on your earthbag building discussions. I'm happy to answer questions, but don't get me wrong...I love and practice all forms of natural building. It's just that me and my partner Kaki wrote this book called Earthbag Building about 6 years ago, so it seems like we're all about EB's. Oh, but there is so much more to learn isn't there?
I'm not here to convert anyone to a particular type of building method or material. As permies know (and natural builders, too) it's all about climate, environment, location, and availability of materials. Use that which best serves all your purposes.
Ok ok ok...'nuff said...lets get down to the nitty gritty dirt of the matter. Lets dig dirt together!
Doni Kiffmeyer