I don't know if it helps, but I'm using
Trinity 3.5.12 on Debian
Squeeze with the NVIDIA proprietary drivers. I don't have multiple
monitors, but randr seems to work fine. I can resize from the tray
icon anyway.
Using nVidia here as well. In fact, my primary development machines use
nVidia cards. :-)
While nVidia does not have XRandr 1.3+ support (and therefore cannot
handle multiple monitors, etc.) this does not break Trinity. The
appropriate configuration options only become available if the underlying
hardware supports them.
If you really want multiple monitors via XRandr with nVidia cards, try the
nouveau drivers. Be aware that they do not support 3D well at all at this
time however.
Tim