For those of you who have often wondered why ssh X11 forwarding never quite seemed to work right in vservers, the magic incantation is

X11UseLocalhost no

inside your /etc/ssh/sshd_config file in the vserver.

This is because by default ssh tries to bind the forwarding server to the loopback address, and frequently your vservers don't have one :-), changing this option means it binds instead to the wildcard address (so keep that in mind for security :p)