alt + left clicking on the terrain does nothing for me, nor does holding down the middle button of my synaptics trackpoint (which works as middle button elsewhere). Actually, alt+left lets me move the window while holding them down on the terrain and moving the pointer, which doesn't work without alt.
Could this be because of the GDK_NATIVE_WINDOWS=1? I'm running Lubuntu 11.10. and everything else works fine and alt does the right thing elsewhere.
As it is, I have no way to view terrain info, except maybe with an external mouse.