Thanks Kelly, I have done similar things in PhotoShop with layers but since this question was asked and answered quickly and succinctly, I learned to do it in Vegas Pro.

In one project, I had five different blurred faces in the same clip.

If you know an oval, or one of the other regular shapes, will effectively define the required blurred area at all times, then Cookie Cutter is quickest, as Kelly suggests.

If custom shape mask needed, then use Bezier mask in Pan/Crop.

Often, each face or whatever will move within the frame, so Synchronise Cursor and check every second or so and create keyframes to track changes in position and size of mask needed.

To make as subtle as possible, play with feathering edges, in Cookie Cutter or Bezier P/C.

(I've assumed knowledge of some functions, but please ask if amplification would help.)

I've found that a vodka double does the trick for me....

How do you do it in Photoshop and Pan/Crop? Can you apply a blur to a transparent layer? The cookie cutter method is fine, but moving the blurred circle is a pain, with that tiny handle that you have to use to move around the frame. I would like some way that I can click on the face I want to blur on each keyframe.

I like the pixelator effect in NewBlue Video Essentials.

Sebaz, here is a thread where we discussed some techniques for blurring faces a while back.