Snow Leopard users should disable FileVault: If you're upgrading from Snow Leopard (OS X 10.6)
and you're using FileVault, OS X's built-in account-encryption feature on any of your Mac's accounts, I recommend
disabling FileVault before upgrading to Mountain Lion. Mountain Lion, like Lion before it, uses a different (and
much-improved) approach to encryption, called FileVault 2. Apple says you can keep using the Snow Leopard
implementation for previously-encrypted user accounts, but FileVault 2 is the better way to go, and what better
time to make the switch than now? (As I noted in my Lion-upgrade guide last year, I also prefer to not test
Murphy's Law by risking any incompatibilities between the two versions of FileVault.)
Disable third-party disk encryption: If you're using third-party full-disk encryption software,
you may want to temporarily disable that encryption before upgrading your Mac's OS. Most of these products interact
with your drive and the OS at a low level, and an incompatibility with Mountain Lion could leave you unable to boot
your Mac or, worse, unable to access your data at all. Once Mountain Lion is up and running and you've verified
(with the developer) that your encryption software is compatible, you can re-enable encryption. However, given that
FileVault 2 also encrypts your entire drive, you might consider this an opportunity to migrate to FileVault 2.
Run Software Update: To be sure you're running both the latest version of Mac OS X--version 10.6.8, for example, includes fixes
to Snow Leopard that are required for upgrading to Mountain Lion--and the latest versions of any other Apple
software that might be affected by the upgrade, you should run Software Update (from the Apple menu). You should
also check for updated firmware for your particular Mac model.
Check for Mountain Lion-compatible updates to third-party software: As with any major upgrade
to Mac OS X, you'll likely find that some of your third-party software needs to be updated to work with Mountain
Lion. If you take some time to check compatibility before installing OS X 10.8, you'll be in a position to get up
and running immediately, rather than being frustrated by your favorite apps and add-ons not working.
To check app compatibility, you can visit each developer's website, but I recommend first checking RoaringApps'
growing list of Mac software and Mountain Lion compatibility. (The
list shows both Lion and Mountain Lion compatibility--be sure to look at the Mountain Lion column.)