Apparently I have been living in a cave (or in New Zealand). Last time I undertook a memory upgrade to my Mac Pro it was an over-draft extending exercise and I must admit that I noticed bugger all boost in performance. Out of sheer desperation I have just maxed out the RAM on my MacBook Pro (to 8GB*) and on Sarah's iMac (to 16GB) the whole exercise was cheap as chips and the performance increase has been sensational.
I think I should take a little step backwards. It turns out that I was not only living in a cave, I was also living in 2008 (a time when packing 4GB of RAM was worthy of a custom printed T-shirt or bumper sticker) and I had become unaware of the memory demands of Apple's latest iteration of OSX - 10.7 Lion.
Apparently Lion eats 4GB RAM chips for breakfast and our hitherto snappy had Macs become practically un-usable when running Photoshop and Lightroom consecutively after the Lion migration. The Beach ball of doom became my screen saver.
After yet another hard restart I googled the problem and found this handy and revealing post about RAM memory use in Lion on the apple forums.
I purchased my mac memory upgrade from RAM city** and I was really impressed. The transaction was processed in NZ but the RAM was couriered in from Australia and they dealt with all the customs bollocks and freight was at local prices - highly recommended to NZ and Aussie readers.
I have also previously purchased Mac RAM upgrades from Amazon and received equally top notch delivery and product.
If your Mac is dying a death from memory starvation, especially under OS-X 10.7 Lion, do not hesitate to upgrade it's RAM it should boost performance instantly.
Feel free to ask me any questions in the comments stream - I'd be happy to assist.
*I'm looking forward to a 16GB capable (non-retina display) Mac Book Pro update as I am still hitting the limits when sending Nikon D800e files from Lightroom to Photoshop CS6 - especially when stitching panoramas. Why no retina display? cost, and I really want to rip the optical drive out of a 15" MacBook Pro and throw in a second SSD drive using one of these OWC Data Doublers.
**The worst part of buying memory upgrades is figuring out what version of Mac you have....