Enabling Scroll Bars In Mountain Lion?

In Mountain Lion scroll bars are turned off by default, and are only seen if actively scrolling.

How do you enable them, so that they are seen all the time ?

See screenshot. Change the radio button for Show Scroll Bars to Always. To access this screen, go to System Preferences -> General.

Terminal Command

Alternatively, if you like Terminal commands (for scripting or BetterTouchTool gestures), you can set scroll bars to always be shown with the following command:

defaults write -g AppleShowScrollBars -string Always

To reset this, you can use the following command:

defaults write -g AppleShowScrollBars -string WhenScrolling

You may have to restart the app (or Finder: killall -HUP Finder) for the change to take effect.

Per App Setting

As well as being set globally, these Terminal commands can be used to change the scroll bars specifically per app.

defaults write com.apple.Terminal AppleShowScrollBars -string Always

^{Replace com.apple.Terminal with the bundle identifier of the app that you want to change.}