OK, testing as you said above:

xterm launches, echoes DISPLAY
browser (opera) launches, echoes the DISPLAY I set
fmradio - doesn't launch, w/GTK+ can't open display <IPADDR>
vncviewer - doesn't launch, no GTK error, echoes DISPLAY
gpe-calendar - doesn't launch w/GTK+ can't open display <IPADDR>
pwsafe - doesn't launch w/GTK+ can't open display <IPADDR>

So, some apps do honor $DISPLAY and some don't? Am I interpreting that right? But, even if they honor it, they won't export over SSH.