Hi All, I just wanted to share my recent OS X experience for the benefit of others. I've got a 2009 MacBook Pro 15" (2.66 Intel Core 2 Duo) which has severed me well up until now. It's been into Apple under AppleCare for a few issues over the years, but otherwise it is still a very solid machine which meets my needs well. My computer requirements have changed in the last few years as my job has changed, so I rely on this machine much less as a power house for photoshop and video editing and much more as a recreational machine for web/email/viewing video etc. However, since updating to Mavericks I was finding doing just that difficult - even loading a few web pages was causing the machine to beach ball, stutter and splutter! Opening even the most basic of apps became a painful experience which I tried to avoid wherever possible. It was becoming frustrating, so much so that I started looking at new Macs as I had (prematurely) reached the conclusion that the machine's life was nearing an end. Well, how wrong I was. £50-ish of RAM later (direct from Crucial), doubling my memory from 4GB to 8GB has worked wonders. With only a few Safari tabs, Mail, iTunes loaded, my MBP appears to consistently use about 5.4-5.8 GB memory - this obviously means 4GB was not enough for my requirements. My Mac feels as good as it did pre-Mavericks (if not better!) and the machine easily has a few years more use for me. It's clear to me that the operating system really does require 8GB to run a more than one or two processes smoothly. I know it really does seem obvious to the power users out there, but I just wanted to reassure anyone experiencing issues with Mavericks to pop some extra RAM into their machine as it has worked absolute wonders for me with very little cost. My final comment would be that this has really made me question ever wanting to buy an rMBP. Knowing that in future, if I purchased one, I would not have the option to add extra memory as software evolves means I have serious doubts about the longevity of such a machine. I would certainly welcome anyone else's experience of RAM/performance with Mavericks.