If your current usage isn't even close to 8 GB, then 16 GB is a waste of money. I'm not sure where people are getting the idea that having an extra 8 GB will increase the resale value of the machine tremendously because it won't. That extra 8 GB won't be worth even close to $200 in a year from now. It'll be worth like $50. Anything that's made with flash memory will not hold its resale value because the price of flash is rapidly decreasing. Anybody who needs 16 GB of memory in their laptop won't be buying a used one. I think some people are trying to justify their waste of $200 by saying things like "don't get the RAM you need now, get the RAM you need in 4 years". How many people who just bought a RMBP are still going to have it and not the latest model in 4 years? Honestly...
Oooo some common sense.
I use lots of powerful software: Photoshop, Cinema 4D, Logic Studio and 8GB ram is enough, i never feel like i need more and my system is never strained. I am disappointed the RAM isn't upgradable but i still went for 8GB because i know i would struggle to use it, even in a couple of years.
At this moment i have Photoshop with a large document open, Pages, Outlook, Chrome (6 tabs), Twitter app.. 3.98GB free.