I installed OpenBSD on a Sun Balde 1500. X is working on the machine itself (for example with gnuplot and GNU Octave). However it doesn't work through ssh. With my FreeBSD machines I don't get this issue.
G N U P L O T
Version 4.2 patchlevel 6
last modified Sep 2009
System: OpenBSD 4.6
Copyright (C) 1986 - 1993, 1998, 2004, 2007 - 2009
Thomas Williams, Colin Kelley and many others
Type `help` to access the on-line reference manual.
The gnuplot FAQ is available from http://www.gnuplot.info/faq/
Send bug reports and suggestions to <http://sourceforge.net/projects/gnuplot>
Terminal type set to 'x11'
gnuplot> plot sin(x)
gnuplot: unable to open display ''
gnuplot: X11 aborted.
# uname -a
OpenBSD Tiphareth.home 4.6 GENERIC#43 sparc64