Just want to clarify something here. I've noticed throughout this thread that people are referring to the rMBP as having SSD for storage, and even a post stating that it would be the only upgradable part of the computer. I want to point out that the rMBP does NOT have an SSD, at least not as people picture it (1.8 or 2.5 inch HDD looking device). It has individual memory modules soldered onto the motherboard. Thus, unless you feel competent enough to remove them and solder on some new ones (I'm certainly not), your SOL in terms of upgrading them. Therefore, go for the 768 GB and a nice external thunderbolt drive, for quite a nice chunk of $$$ of course.