Probably I should have told that my client system is
Ubuntu 12.04 GNOME3 Classic (no effects) X2Go Client V. 4.0.1.1
and the remote is
Linux Mint 12 x2goagent 2:3.5.0.20-0~340~oneiric1 GNOME3 (Command: gnome-session --session=gnome-fallback)
Is it the remote system's GNOME3 that is the culprit here? I didn't have resolution problems when my local screen was 1680x1050.
--
Timo