While i'm all for high density displays, I would much rather have the extra screen space of a 1680x1050 MBP than a 1440x900 display at double the resolution. One gives me something tangible and usable, while the other gives me prettier fonts when I have my face close to the screen.
My laptop, at its
closest to my face is still a foot and a half away. Normally it is 2 feet away. And this is an 11" MBA, which has the highest PPI for any Apple notebook right now. It is also the smallest, which means I use it closer to my face than any other laptop. When I had a 15" MBP it was always around 2 feet from my face, and that was with the high res display. I can still see pixels if I look hard enough, but for the most part at over two feet I can't discern pixels in a 12 point font at the 135 PPI of a 11" MBA.
I enjoy the difference in the iPhone 4/S and would love a retina display iPad, but I really don't see the point in a laptop. iPhone went from 163 PPI to 326 PPI with retina, but when I use my iPhone it is always around a foot away from my face. I don't feel the cost difference plus power difference will be justified (4x more pixels means smaller pixels, which means a more powerful backlight is needed to get the same brightness levels.)
Ultimately I would rather just have a 15" MBP with a 1920x1200 screen option with more scalability built into OS X. But if not I will wait until the Retina displays come in "high-res" models (3360x2100). Or if there is a 13" MBP with a pixel doubled display at normal resolution 1440x900. I can live with that
My point is if you are going to have a super detailed display, it should already display a lot of information. Text and icons at 1440x900 (110 PPI on the 15") are gargantuan compared to the 135 PPI of a 11" MBA. Double the pixel density of the higher res display as it will give you better readability while also giving you more usable screen space.