Real nice, if the person is sitting in one place, but what about if the person is moving around, say walking away? I don't think that the blur will follow the person.
Well, in this case I think it will get a little more complicated and too expensive for just a hobby,youtube video or something like that. http://www.geniusdv.com/weblog/archives/creating_mask_to_blur_out_a_face_with_avid_xpress.php Adobe Premire can do that too.