I asked a similar question here:
http://bushwalk.com/forum/viewtopic.php?f=15&t=5128. Not on the same level as Kokoda. But along the same lines
I've since used the poncho a bit and it has kept me the most dry on the inside out of anything I've tried (haven't tried event or goretex) in the rainforest. I sweat alot.
As mentioned it probably isn't necessary to stay dry in warm climates as far as safety goes but I think it is still nicer and more comfortable to stay as dry as possible. Even if the temp is reasonably warm, if there is a fair bit of wind plus rain it can be pretty miserable.
Just make sure you have something dry to sleep in and some way to store wet clothes overnight.