Comment 4 for bug 865515

I agree the default of nat is appropriate for desktops and I feel quite strongly it should not change there. The default for servers is probably better as non-nat (though this could be debated), as this bug suggests. However having different behavior depending on the type of system it is would likely cause confusion. Perhaps it would be appropriate to add a preseedable debconf question to allow proper setup of the bridge for servers. This could be of priority 'medium' so desktops don't get prompted, but server environments (which would arguably use preseeding more often) can set debconf as part of installation. Admittedly, this is not perfect, but might help.

My 2 cents