A feature which I've come across that seems to be relatively hidden in Mountain Lion and not noticed by many others is the ability to encode videos with Finder.
I remember the only way to encode videos was with third party apps such as Handbrake. But with Mountain Lion you can encode most videos so they work with Quicktime and iOS devices.
The encoding feature is built-in to Finder but it seems to be hidden away and not put in plain site.
Simply CTRL+click (right-click) on the video you want to convert, then go to "Services" and select "Encode Selected Video Files".
You'll be shown the window above and you can choose your required settings.
It's a brilliant feature which I think should be noted. It's very useful and can help you make your videos compatible with your media devices such as iDevices and Android devices.