Little more testing.... It seems to depend which app it is. If I run vncviewer, gpe-calendar, pwsafe, fmradio, and most others, they launch and display on the n800 (this is with ssh -X, and DISPLAY still as 0.0).

browser and mediaplayer-ui, on the other hand, don't launch, and just drop back to a shell.

Now, after manually setting $DISPLAY to 10.0 (export DISPLAY=':10.0') during the same SSH session, fmradio fails with Gtk - cannot open display:, as do pwsafe and gpe-calendar.

Vncviewer just returns to a prompt, no error. The browser and mediaplayer-ui just return to a prompt also, no error.

So, it appears that $DISPLAY is honored, at least by most apps, but something else is going on to prevent them from using it.

Edit: This is all as user, no "sudo su" or ssh -X root@n800 that could be confounding.