I thought I'd blog this just in case someone else is having problems using XQuartz on OS X as a server to remote X11 applications (i.e. using ssh -X somehost).
At first this works but after some time (20 minutes, to be exact) you'll get "can't open display: localhost:10.0" errors when applications attempt to connect to the X server. This is because the X forwarding is "untrusted" and that has a 20 minute timeout. There are two solution here: increase the X11 timeout (the maximum is 596 hours) or enable trusted forwarding.
It's probably only best to enable trusted forwarding if you're
connecting to machines you, well, trust. The option is
ForwardX11Trusted yes and this can be set globally in
/etc/ssh_config or per host in