In my opinion the extra real estate greatly outweighs lost mouse
pointers and I lose mine all the time. Not to mention looking at one
screen and finding out what I typed appeared in a window on the other
I need window focus to follow my eyes. :)
(Off topic, but here's a simple way to locate the mouse pointer in Windows)
Open Mouse Properties, click the Pointer Options tab,
Check the checkbox that says 'Show the location of pointer when I press the
CTRL key' and click Apply.
Now press the CTRL key - you'll see that it now produces a bulls eye over
the mouse pointer each time that CTRL is pressed, making it easy to locate.