Since now we see attacks from inside intranets, using zombie networks, I think it could be a good idea to turn on the firewalls on each machine in the network (including on Windows stations, which I know is sometimes a problem) and to set up a detailed set of rules for them.
My problem was: how to figure out which rules for such a complex problem, so many machines?
My suggestion: why not propose a standard for a single file giving the positive rules necessary for a software to operate?
One file per application, that would come shipped with the application, and would describe all the things that need be open, for the application to work. The file would not describe what set of rules to put on which firewall, but simply what needs to be open.
If we have a look at the TCP/IP layers
I guess a simple XML dialect could be created to describe which things need be let in and out, on which layer. If this gets standardized or at least RFC'ed, there is a good chance to see opensource software adopt it, both on the application and on the firewall sides. On which case, since opensource is biggest marketshare on infrastructure, others should follow.
(All that raw and unrefined.)