There is an interesting article at TechRepublic about GNZ or Global Name Zones in Windows Server 2008.

http://blogs.techrepublic.com.com/networking/?p=608

For the record, in the Windows Support Tools, you can find the browstat.exe utility (browstat status from a command line) that allows you to check which computer is the Master Browser and then to troubleshoot that mess that is slowing down your LAN.

Enjoy!