Skysail, (was your dad a studding sail? Sorry, couldn't resist)

I'm pretty late to this party, and you have already gotten pretty much the same advice I would have given (the good part of it, anyway). I'll just confirm from my own experience.

I have used ponchos as shelter since the late 1940s (no money for anything else, and mil surplus was easily available, plus, tents in those days were godawful heavy). Used them often as Pica describes (and still do sometimes if I trust the weather), once in awhile with a friend we used two like shelter halves (snapped together, military poles). Later there were lighter military ones, and then syl nylon.

The one I use now is slightly oversize custom from MLD. Weighs a bit over 300 grams (about 12 oz). In some cases of hard rain I use it for rain gear, but mostly it's my shelter. I have dedicated lines with tighteners and quick snaps and I carry titanium stakes. I can have it up in the half-pyramid mode in a goodly wind (with a hiking pole) in about a minute.

But as others have noted, I actually carry a very light rain suit and a very good bivy. The top of my rain gear is also my windshirt, and the pants I wear at the laundramat (as well as in driven cold rain--which the poncho handles poorly), plus they are the only long pants I have (important in cold wind). And the top allows me to get back into my sleeping bag dry after a midnight trip in the rain.

The bivy, also from MLD allows me to pitch the shelter lean-to even when I'm not dead sure that wind direction will hold. Also keeps out condensation if I pith the poncho low and tight. Wouldn't want to use just the bivy alone out in the open in rain (how do you get in and out, change clothes, cook, etc.--though I did do an AT thruhike with one of the heavier ones alone) but I think it's necessary with a very small tarp. The bivy weighs 180 grams (about 6 oz.).

The whole shelter system (including cords, stakes, plastic ground sheet and stuff bags) comes to 660 g (about 24 oz). Today, one could find a real tent for the same weight (though at frightful expense), but, like Lori, I like the openness and flexibility of my system, and hell, I'm used to it. Never really could get used to tents. best, jcp