Yep, as Wandrinstar said, with the cocoon fully shut and no ridge line in I was not happy about the condensation build up, but this was right in my face, so I rigged up the additional ridge line and I felt it was fine like this, I stopped out on quite a cold night without finding excessive ammounts of condensation, the head vent helps alot in my opinion.
Even if you do find you are suffering with excess condensation as it is a synthetic you could just leave it open to air during the day and it wont effect the loft that much.
I am posting the cocoon to a chap in Scotland for him to give it a try too, so lets see what he comes back with, but as I have said I am impressed and have my name down for one.