Rating: 4 / 5
I suppose someone had to review the Z-rest. I bought it in 2003 before it was renamed "Z-lite" and the price was doubled (it was a reasonable $15 at the time). It has a number of positive qualities: it's very durable; I can whip it out anywhere and lay down. It has an extra coating on the bottom that resists abrasion and puncture very effectively. It doesn't absorb water because the foam is sealed. It is accordion-shaped so it makes a great back pad in my frameless Golite Gust. It is also very easy to pack up for the same reason.
There are some significant drawbacks, however: the weight/R-value ratio is higher than some other pads such as the CD Ridge Rest. I also hear that the Ridge Rest is more comfortable. The "eggcrate" pattern on the Z-rest is pretty much a joke once you lay on it; any significant pressure flattens it completely. It may add something to the insulation in places where your body places little weight on it, for example under your arms.
So I give it good marks for convenience and durability, average marks for warmth/weight and comfort.