Uhm - I said 2nd monitor. And no graphic designer will use a $200 monitor. Might as well go PC. (You can get an awesome 24" Cinema Displays on CL for < $500).
My point was that you lose portability when you must be tethered to a monitor that works.
What are you talking about? Plenty of graphic designers will use a $200 monitor (especially a Korean IPS). Some even use TN panels so they can design an image in the way that it will be perceived by most consumers.
I don't know why a professional graphics person would use a monitor with no controls except for brightness (other than "to see what consumers see"). Having control of the contrast and colour levels is vital for calibrating a monitor, which is something that everybody with a professional interest in visuals should do.
My point was that you lose portability when you must be tethered to a monitor that works.