I looked at 16GB originally when I first bought this MBP after the demise of my long serving previous MBP.. but decided that the update from 4GB to 8GB was better at that time than the ridiculous prices they charged for 16GB.. now with time 16GB is reasonable and so I took the plunge.

Firstly everything is naturally quicker.. now HD limited on initial loading but after that everything is in memory making the machine pretty much instantaneous in normal use.. however this also means that compiling is exceptionally quick and processing large sets of images (stacking and the like) is lightning fast with the i7 running maxed out without waiting for the HD.

So for ~£100 for 16GB (Crucial memory) for my early 2011 MBP this is a great move :D Most people would be fine with 4GB.. APers need a bit more ram and 8GB is a good size to help stacking etc.. 16GB still offers good additional gains in performance.