Today it is only possible to do copy cataloguing from Z39.50 sources. Making it possible to get records from SRU sources would be a nice addition.
(What prompted this bug report was the fact that BIBSYS, the common catalogue for Norwegian academic and special libraries (and an invaluable source for copy cataloguing), stopped supporting their Z39.50 server as of May 1st 2001. It is still running, but if it fails it will not be brought back to life again.)
*** This bug has been marked as a duplicate of bug 6536 ***