One concerning thing I have noticed with breathable membranes (tyvek etc) is that they don't have the self-sealing qualities of bitumen felt around nails.
It appears that there will always be a slight gap around any nail or staple which penetrates the membrane, and if the membrane flexes a little, then any such gap gets a little bigger.
So is this a big issue, and could it lead to water penetration under the right conditions?
dg