I found the following bugs in the version 6.0 (dated 961229).

At least the first two should be fixed before the final release of 6.0.

1)      There is a mismatch between the type declared in the catalog for
        the input/output attributes of pg_type and the actual type of
        values stored in the table.  The type of typinput, typoutput,
        typsend and typreceive are declared oid (26) while the values are
        regproc (24).  The error was there also in previous versions but
        nobody noticed it until an Assert has been added in ExecEvalVar.
        The effect is that it is now impossible to replace the typoutput
        of existing data types with new procs.

2)      The identd hba fails after the first time because the data read
        from the identd socket is not zero-terminated and strlen reports
        an incorrect length if the stack contains garbage, which usually
        happens after the first connection has been made.

3)      The new initdb wants to create itself the data directory. This
        implies that the parent directory must be writable by postgres and
        this may not always be desirable.  A better solution would be to
        allow the directory to be created by root and then filled by initdb.
        It would also nice to have some reasonable default for PGLIB and
        PGDATA like the previous version did.  This applies also to the
        postmaster executable.