smbclients outputs always the server banner:
| $ smbclient -d0 -k //cricetus/test3 -c 'ls' > /dev/null
| Domain=[XXXXXXXXXXXXXX.DE] OS=[Unix] Server=[Samba 3.0.33-3.28.el5]
That's bad because it makes difficult to write cronjobs which shall be quiet on successful operations and return error messages on problems.
this alone wouldn't help you very much for cron jobs. smbclient does not write things like
NT_STATUS_NO_SUCH_FILE listing \file_that_does_not_exist
on stderr. Also a failing -c "command" doesn't result in smbclient setting return code != 0. I'm not sure if this is actually desired to be so.
yes; I filed some other reports (e.g. the return code == 0 on failures is bug #7551). Good catch about the output of error messages on stdout instead of stderr.