Very true and important to state, UUIDs on their own at most provide obscurity, not security.
Can the MAC address of the host that is used for some versions be extracted/read from the UUID or maybe inferred by observing a number of UUIDs?
I think people may be misled by the fact that UUIDs are frequently hex-encoded prior to being sent over the wire (or even, stupidly, in the database). It looks like a hash, but it's very much not one.
Edit: This is all referring to RFC 4122, to be clear. It's entirely possible that there are some other UUID schemes out there which do hash their contents.