Eric Richardson, who works on CMS, has this unnatural fear that a UUID (or GUID for you MicroSofties) may collide with a GUID generated on another machine.
I care about GUID consistency. Nobody should be putting images directly into the Resource Gallery in Production. Those have to be migrated, whether or not they are used only in Production. Here is why. If some things go into Test and are migrated, and other things go just into Prod, there is a chance that the GUID will end up being the same for an item already in Prod and one getting migrated.
I hate having to educate people, especially since they are so wrong. To save you the trouble of sifting through the draft, here's the short of it:
UUIDs are generated from a very precise (100ns) timestamp and the node id. If you don't have an accurate clock, you use a "name" which is supposed to be as broad as possible, including DNS addresses, machine name, etc.