Pretty straightforward face blurring that uses manual tracking.
This second tutorial mentions some keyboard shortcuts you can use to speed up the process.
Finally, here is a tutorial on auto tracking for “painting out” a detail on a moving person. You could replace a blur for the paint which you could use for a complex moving path that needs to be blurred. This tutorial is a good introduction to tracking if somewhat fast! The GeniusDV tutorials are very quick, so watch them multiple times to get the gist of the procedure. Good luck!