In reply to The Lemming:
A friend of mine has one of these
http://www.fatboyusa.com/us/lamzac and I've used it a few times.
Once you get the knack of inflating it (which is a bit of a black art), they pop up in seconds and are very comfy for both lying on and sitting on.
They are made of some fairly tough rip-stop nylon with a plastic liner and seem a bit more resistant to puncturing than the standard plastic jobbies.
Cheaper imitations are now available but I can't comment as to their quality or reliability.
