Show Active Screen Corners

A nice hidden feature in 10.3 which I found out. With
defaults write com.apple.dock wvous-showcorners -bool true
you can make the dock show the active screen corners like this:

Of course you have to killall Dock or logout and in again for it to take effect.

A more convenient way to activate it:

1. Click to enable dock corners
2. When Script Editor opens, click the green run button

Click Disable dock corners to disable it again.

Sadly this doesn't work with multiple displays.