I thought long and hard about this one, and eventualy ordered 16Gb... Then. Apple called me two days ago to say they had 8Gb in stock and would I like one. I needed to make a decision, so decided to run a test on my existing Mac to see in a worst case situation how much RAM I would use....
The answer was 5Gb. I am now typing on my new Macbook Pro Retina 8Gb, and amazed by its performance.
8Gb is enough, if I sell within 3 years then I will not recover my investment into 16Gb that I will never use.
Same thing here got one in stock had one on order for 16 gb base, I can even do better I compared my quad core IMAC i7 with 16 gb and final cut pro x and this will make you feel better, I threw FCPX and motion and after effects on both machines, and the retina actually finished my render 5 seconds quicker. Actitivity monitor showed the IMAC taking more ram but the 8gb didnt perform slower, there is more than meets the eye and the activity monitor does not tell the whole story. Inactive ram is pretty much unused ram and I was eccastic with the performance of this machine and will not be returning it. 16gb is overkill by the time I might ever need that much ram Ill probably be buying another computer so Id rather have that money go towards that future purchase rather than the ram upgrade. Truth is two years from now we maybe in different territory as far as graphics and processing power goes, faster SSDs etc, so the ram will be the least of your worries. This machine is amazing!! Love it!