After spending almost a month on the road using only the retina screen on my MacBook Pro, I was in for a harsh reality check when I connected my Thunderbolt Display earlier this week. I immediately noticed that text wasn't as crisp as on the portable. I normally run my MacBook Pro's screen at a resolution that Apple calls "More Space", giving me the maximum amount of screen real estate on my Mac. I didn't think I would much notice the higher pixel density when running in this resolution, but I couldn't have been more wrong. DPI is king, and makes all difference! The MacBook Pro comes in at 220 dpi (dots per inch) while the Thunderbolt display only has only 109 dpi. For comparison purposes the iPhone 4/5/6 all have screens with 326 dpi.
I second many in their wish for Apple to produce a HiDPI external display like the Thunderbolt Monitor. I suspect we haven't seen these yet due to many problems including bandwidth on existing hardware, graphics performance in portables, and screen costs. Will 2015 be the year?