I don't have time now to read through all the posts in this thread but... are you guys familiar with this lightweight two persons vivac/tent?
ALTUS GORIZ
Ponchos, tarps and alike are ok if you don't have anything else, but... if you are actually planning to sleep outside and still want to go ligthweight, I think nothing beats this kind of shelter. You are not even forced to use trekking poles, you can also stretch it with some cord between the trees. It only weights as much as a full water bottle (1,1kg). Well, a BD or NorthFace GoreTex fabric tent will probably do it, but again, will be a tad heavier and a hell lot more expensive.
Mikel
ALTUS GORIZ
Ponchos, tarps and alike are ok if you don't have anything else, but... if you are actually planning to sleep outside and still want to go ligthweight, I think nothing beats this kind of shelter. You are not even forced to use trekking poles, you can also stretch it with some cord between the trees. It only weights as much as a full water bottle (1,1kg). Well, a BD or NorthFace GoreTex fabric tent will probably do it, but again, will be a tad heavier and a hell lot more expensive.
Mikel