Before updating to mountain lion
A good list of compatible and incompatible apps is maintained in a searchable database by Roaring Apps, check it out here.
If you find apps that are incompatible with OS X 10.8 you can either find an alternative on the App Store, or consider holding off on the system upgrade until the developer gets their act together.
Or as the old expression goes "pioneers take the arrows, settlers take the land." The problem with major OS updates like 10.8 is that they break things.
And nothing's worse than installing a major update like 10.8 only to find out that one of the apps that you use daily now crashes on launch, or won't connect to the Internet.
Some older devices are compatible, but won't support certain features.
Apple has made it easier than ever to update to the latest operating system, even if you are running an older OS X operating system on your Mac.
It also tells you how to work out what is the newest version of OSX that you can run on your computer.Another thing to consider is that 10.8 was relased to the public This means that developers have only been testing their applications against 10.8 for just over two weeks -- assuming that they downloaded the GM on the first day it was available and that they've been testing every day since.Method 3 gives you a thumb drive that you can use multiple times to install OSX, and you can even boot off it in an emergency if your hard drive crashes.Before you get too excited, you might want to make sure that your Mac can actually run Mountain Lion.Fortunately, Apple has published a complete list of which Macs will be able to upgrade (and in turn, which Macs aren’t compatible).