For instance, CouchDB includes a resource, /_uuids, that returns a number of server-generated UUIDs. As far as I know, it only exists to support languages without a decent UUID library. It has no effect on the server.
However, CouchDB will only respond when /_uuids is POST'ed to:
$ curl -X GET http://localhost:5984/_uuids?count=2
$ curl -X POST http://localhost:5984/_uuids?count=2
One suggestion on the mailing list (although not from one of CouchDB's core developers) for the use of POST is to, "comply with REST as it returns a different output each time".
A GET would be just fine here. In fact, it would be more in keeping with the intended use of the HTTP methods.
It's easy to come up with examples of a REST-ful resource that sends a different response every request, with probably the most obvious being some sort of time server. Consider the following URLs: