As we know, Apple made a new MacBook category, called MacBook Pro with Retina Display for over one year now. So when Apple held their iPhone keynote, they also updated the MacBook with RD while they were at it.
The new MacBook Pro with RD features a razor sharp screen. The screen has 4-5 million pixels, depending on the model, which makes it impossible to see any individual pixels.The new MacBook has also got the latest generation of processors from intel. You can get a i5 or i7 processor, depending on the model, ranging 2.8 - 3.3 GHz. That is some serious power packed in to the beautiful aluminum body.
Next up is Intel Iris Graphics. Now the new MacBook With RD, has 90% better performance. This means that the MacBook can now handle complex tasks with ease, like gaming, watching a movie or simply completing every day tasks. Combined with NVIDIA GeForce GT 750M the graphic should be absolutely amazing.
The last upgrade that I want to mention is the battery life. Although Apple has made the MacBook With RD even more powerful than the previous generation, they managed to increase the battery life to 8hours for the 15 inch MacBook and 9 hours for the 13 inch one. 
And of course it comes with Mavericks;)