There are a few silverlight demos that use the InkPresenter, though two of them don't refer to Ink at all...:

The page turning demo has it. You can annotate the pages and that gets remembered during your session. As you flip the pages back and forth, the annotations are incorporated into the effects.

The scribbler demo has it. This is straight drawing. What I love here is the cool pallette.

The Ink Tattoo Studio demo has it. This a fun demo.  On a tabletpc, the pressure of the stylus can be registered by the digitizer.I saw a version of this app that said "Ouch!" if the pressure got too high. Otherwise, the tattoo tool buzzes.