What everyone widely expects from Retina display Macs is an iPhone or iPad-style resolution doubling. So if the current 15-inch MacBook Pro has a 1,440 x 900 display, the Retina 15-inch MBP would have a 2,880 x 1800 display.
What the rumor mill is missing is that there’s no benefit to Apple handling a jump to Retina display Macs this way. The reason the iPad and iPhone going Retina was such a big deal was because they had really pixellated displays. Before the iPhone 4, the iPhone had a display that was only 53% close to being Retina. The iPad was slightly better, at 61%. Roughly, both the iPad and iPhone were only about halfway there, which made the easiest fix to just double the amount of pixels per inch.
But Apple doesn’t need to do this with its line of Macs. In fact, it’s likely that most “Retina Quality” Macs will have fewer pixels than your new iPad.
Smart analysis. Mac OS X scales really well, unlike iOS, so it will adapt to however many pixels Apple throws at it.