I find that X11 forwarding over ssh does not work on SL 4.4. I get the message
_X11TransSocketINETConnect() can't get address for localhost:6011: Name or service not known

I found a workaround at:
http://bugzilla.mindrot.org/show_bug.cgi?id=164

which is to add the line:

::1 localhost
to /etc/hosts

apparently it is something to do with having both IPV4 an IPV6 available at the same time.

The place I found the workaround is a discussion of the bug from 2002 claiming it is now fixed!

  cheers,

  Alex Finch