Snow Leopard users only: A bigger issue may be older Mac software that hasn't been updated recently--you may find that it doesn't work at all under Mountain Lion. Specifically, PowerPC programs--software that was never updated to run natively on Macs with Intel processors--won't work at all under Lion or Mountain Lion. Under previous versions of Mac OS X, Apple provided software called Rosetta that allowed PowerPC code to run on Intel Macs. In Snow Leopard (OS X 10.6), Rosetta was no longer installed by default, but the OS would offer to download and install Rosetta if you tried to run a PowerPC program. However, Apple killed Rosetta completely when Lion was released, and it remains unavailable in Mountain Lion. If you've got important PowerPC programs (for example, older versions of Quicken for Mac are still surprisingly popular), you'll want to update those programs to Intel-processor versions, if available, before upgrading to Mountain Lion. If such updates aren't available, you should find acceptable alternatives, whether those are modern Mac alternatives or, if need be, Windows versions that you can run under Boot Camp or virtualization software such as Parallels or Fusion. (See my colleague Christopher Breen's series of articles on Lion and PowerPC software.) Alternatively, you could keep an old Mac on hand to run those apps when needed.
How can you tell which of your applications are PowerPC programs? The easiest way is to launch System Profiler (in /Applications/Utilities), select Applications (under Software in the sidebar), and then click the Kind column header, which sorts the list of applications by processor type. Any programs listed as PowerPC will not work under Lion or Mountain Lion. (If you've got any listed as Classic, well, that ship sailed long ago.)
Set up your iCloud account: In Lion and Mountain Lion, iCloud, Apple's cloud-syncing service, is integrated into many apps and system services. To avoid being hassled about iCloud syncing when you first log in to Mountain Lion, simply make sure that you're logged in to your iCloud account under Lion, and that you've enabled syncing for the various types of supported data, before upgrading. (If you're upgrading from Snow Leopard, you'll have to log in--or create an iCloud account, if necessary--once you boot into Mountain Lion for the first time.) For more on this issue, check out Macworld senior contributor Joe Kissell's excellent Take Control of Upgrading to Mountain Lion.
Maybe have an extra drive handy: While most people will simply install Mountain Lion over Lion or Snow Leopard, there are situations in which you might want to install onto an empty drive. For example, if you want to install Mountain Lion on a second drive to test the OS before upgrading your main drive, or if you want to erase your Mac's startup drive and start anew. (The latter might be a good idea if your Mac has been having issues, or if your drive is nearly full or in need of repair.) As I'll cover in an upcoming article on installing Mountain Lion, installing onto a secondary drive is simple. However, erasing your Mac's startup drive and starting fresh means having a good, tested backup (see above) as well as a bootable Mountain Lion install drive, so now's the time to start preparing.
Ready and waiting
Thanks to the Mac App Store, the process of purchasing, obtaining, and installing Mac OS X is faster and easier than ever--Mountain Lion inherits Lion's advantages over optical disks and mail-order delivery. But the better shape your Mac is in before Mountain Lion arrives, the better experience you'll have during and after the upgrade. Now that your Mac is properly prepped, stay tuned to Macworld--once the new OS is officially released, we'll have a slew of articles on installing and tweaking it.
[Dan Frakes is a Macworld senior editor and a compulsive installer.]
This story, "Get your Mac ready for Mountain Lion" was originally published by Macworld.