One reason I got the 171N is the narrow screen margin of only ~ 1cm ("N" is for narrow). So there's about a 2cm gap between the live area of the screens.
I've been using twin-head systems for around 10 years now and have completely trained my vision system to ignore that grey band. (It used to be harder - I started with twin Sony Trinitron 21" monitors that had about a 3" gap between the two live areas).
I have a standing joke that one day I'll be driving my car and will go smack into a power pole, because it'll be a thin object in my central "dead" zone and I'll ignore it until it becomes too late!
There are some limitations. Some apps can't span that many pixels. Some can only display on the primary monitor (PowerPoint and DVD viewers, f'rinstance). One of my graphics utilities can only capture from the primary screen.
Some apps can span both screens easily (if you're a geek, you gotta see excel spread over 2 screens!).
SOme examples:
This reply
My Mars Wallpaper
PowerPoint
(Must get a better digital Camera - this old Kodac DC200 is archaic!
Space/Science » in reply to re: Thanks very much!
Gaps in vision