OK, I updated my posts with Big Sky's numbers and the Nallo 2. Now, getting back to my original post, I again ask (rhetorically this time) if the standard ultralight approach makes sense. The standard ultralight approach is that while a double walled tent makes things a bit warmer (and offers other advantages which, for the moment, we will put aside) the difference in weight is too large -- you are better getting a heavier sleeping bag, rather than a double walled tent (for relatively mild conditions -- no snow, mild winds, infrequent rain). For most of the items on the list, I think this is true. The only items where the double walled approach might actually be warmer is maybe the Terra Nova Photon (for one person) or Stephenson's warmlite 2R (for 2).
Fully enclosed single walled single person shelters seem to range from about a pound to a pound and a half. This makes the photon only about 2 to 8 ounces more. Eight ounces more insulation in your bag with a single walled tent would probably be warmer, but I doubt two ounces would.
Similarly, if the Stephenson's Warmlite 2R is really only two pounds twelve ounces, it is quite warm for the weight. With the exception of the Refuge X, most of the two person tarp tents are about two pounds, making the Warmlite only twelve ounces more. Spread between two people, this adds only six extra ounces of insulation. This may be enough to make the single walled tent better, but I would be curious as to how often the phenomenon Will Rietveld mentioned occurs. Does it occur with various temperatures? Does it occur when it rains or when it is dry or both?