Joel Oleson has once again provide us with very usefull links and overviews on the subjects of Global and Multi farm deployments. Besides the links related to Global deployment, Joel also has some explanations on:
Comparison of WSS 2.0 and SPS 2003 vs WSS 3.0 and MOSS 2007
SSPs and the WAN
Authoring -> Production
Dev -> Test -> Staging -> Production
You can find this article here.