I'll take an alternate view on the tube tent, but agree with the ponchos.

I think the tube tent, which is basically a tube of plastic sheeting, has too many alternate uses, e.g. ground sheet, waterproofing storage for equipment, etc etc etc, to be left behind. I don't think of it as a shelter, rather I think of it as a general purpose item that can also serve as a very quick shelter: open and get everyone inside, even if not put up in the "typical" way. Plastic sheeting is always something useful to have around. I carry a small roll of plastic sheeting in my car all the times.