When you're just configuring a single server, having a static IP address for your server image isn't too important, but when you're configuring multi-server setups, it can be useful to duplicate a number of server images and give each a static IP address so you can consistently deploy to them. While not documented well at all, it turns out that this is relatively easy to accomplish in four simple steps.
Let's say you have a guest machine with the name ubuntu-lucid-lynx-base and you keep your guest machine images in ~/Documents/Virtual\ Machines/. To determine the MAC address for this VM, you can run:
cat ~/Documents/Virtual\ Machines/ubuntu-lucid-lynx-base.vmwarevm/ubuntu-lucid-lynx-base.vmx | grep ethernet0.generatedAddress