Building off of the Arduino port of some of the VUSB code (http://code.google.com/p/vusb-for-arduino/) - I was able to setup a simple, very basic keyboard library for use with the Digispark.

Take a look at the example DigisparkKeyboard→Keyboard

It is essential that DigiKeyboard.update() is called at the beginning of the loop to maintain USB communication, otherwise you can use buttons, inputs, etc to trigger the keystrokes.

For the example: Upload and then place the cursor in a text area, watch it type.

Some ideas: Print out the results of a sensor, say the temperature. Print those results only when a button is pressed. Use it to build an arcade controller. Use it for a password generator.