What the cynic in me finds interesting in Retina displays is how people will tend to hit their data caps more quickly on their mobile plan merely because they are downloading more pixels.
Surely the caps will increase in size as a consequence of improved mobile-data-pushing-technologies and to keep up with the need, just like the speeds of broadband-connections have since they were introduced?
Also, its about damn time we have high dpi displays, we've been stuck at 72/96dpi for far too long on regular computers. I welcome this change and all it brings.