Edd,
I have this exact same problem on my entire campus. 2 seperate domains, several Windows 7 images, deployed to students, staff and faculty. All of the machines show the same NETLOGON error in the event log. I have worked with the Networking group here to get resolution and the only other solution we have come up with aside from what you wrote above is to use a static IP instead of using DHCP. I was thinking about call Microsoft myself to report your findigns and mine but I just haven't had the time yet.
Let me know what more you may need to support the business case to get Microsoft to create a hotfix.
Thanks