When it comes to memory upgrades, Apple's CTO offerings for its Mac systems are options I recommend people avoid, not because of any quality issues, but because of the ludicrously high prices Apple charges for the upgrades. For instance, Apple ships its iMac systems with a standard 4GB RAM, but if you want the optional 8GB or 16GB RAM upgrades, you will pay $200 or $600, respectively.
These prices are more than four times the cost of most other similarly sized and specced RAM upgrade options, which are just as compatible with your iMac as Apple's RAM. While some might assume Apple's memory upgrades are somehow special because of the price, the truth is the memory is no different than that supplied by any other manufacturer, and provided the specifications are the same, a cheaper third-party RAM module should work just fine in your system, and save you an immense amount of cash.
For instance, in looking at the $200 Apple charges for an 8GB upgrade to its iMac systems, you can purchase a similar and compatible 8GB upgrade of Mushkin memory from NewEgg for $45. If you don't like Mushkin, then you can find similar specced RAM from other manufacturers for a similar price. The difference gets even more drastic with the 16GB upgrade, which from Apple will cost you a whopping $600, but if you use a third party, the RAM upgrade will cost you around $100.
Not only does Apple charge a premium for RAM (far more than it does for other CTO components like hard drives and GPU options), but it also does not offer all RAM options its systems are capable of. In its MacBook Pro lineup Apple offers a maximum of 8GB RAM, even though the systems can take up to 16GB. Likewise, Apple's iMac systems are also advertised and sold short of their true RAM capabilities. Starting in mid-2010, Apple's iMac systems support up to 32GB of RAM, even though Apple claims the systems can only be upgraded to half that amount.
It is unclear why Apple claims these lower capabilities of its systems. Perhaps it is simply a matter of testing done on Apple's part, but if you have one of the newer iMac systems (starting in mid-2010), then even though Apple claims you can only put up to 16GB in the systems, you can install 32GB if you wish to maximize the capability of your new system, and do so relatively cheaply.
Recently, Mac upgrade manufacturer and peripheral distributor Other World Computing released a new 32GB RAM upgrade module for iMac systems, which should be compatible with mid-2010 or later iMac systems. The upgrade is priced at $349, and as such is more than $250 less than the price Apple charges for its 16GB upgrade.
OWC's RAM upgrade is a solid option for iMac users to consider, but even it does not beat the available options out there. A quick search shows that if desired, you can get a similar 32GB RAM upgrade from G.SKILL for $100 less than OWC's upgrade.
As with any servicing to a computer system, the idea of upgrading the computer's memory may sound like a technical procedure; however, memory upgrades on Mac systems are one of the few user-serviceable options for which Apple provides detailed instructions. Upgrades simply require you shut off the system, open a latch or remove part of the case, and then swap out the old memory modules for the new ones. Then close the case and start the system -- the process is easier and less painful than even hard-drive upgrades.
The only extra step that I recommend everyone do following a RAM upgrade is to thoroughly test it, which can be done using third-party utilities like Rember, or with using Apple's built-in hardware tests.