Sometimes, programs run in a GNOME terminal window will use xterm
control sequences to request mouse events.  Unfortunately, this
results in it being impossible to use the mouse to select text for
either selection or clipboard copy/paste into another program, since
the relevant events are being diverted.  Having each program support
resetting the terminal mouse on user request might be nice, but it
would also be nice for the terminal emulator to let the user override
this on a temporary basis.  (This would probably be provided on the
context menu, since right-clicking is the one mouse event that is not
diverted.)

gnome-terminal imitates xterm sufficiently in this area that it treats
shifted mouse-events differently from unshifted.  (Perhaps gnome-terminal's
users would find a dialog selection simpler than pressing the shift-key).