As of this morning, Apple Mac OS X Mountain Lion now available directly from the Mac App Store on your computer. There are many new features. You can learn about them all at Apple's Mountain Lion information page.
Apple also has this video detailing the new features.
The folks over at Tested.com also have a feature review video on YouTube.
I will probably be upgrading soon so I can share my experiences with my clients. Watch this space and the TechnologyIQ Twitter account, @techiqpod, for more updates.