So.. just discovered something that isn't detailed in the help file (unless I missed it)... using USER Annotations to quickly assign faces in the viewer.
Let's say you run face detect across a group of images and it only marks 2 of 3 faces in the image. You can go ahead and draw a face box, assign a person to the face and rinse/repeat across the image and or future images. However, another method is to save the person region to the User Gallery.
Right click a known face in the viewer and choose the "Save to Gallery Option". You can name the file with the name of the person and it will then show a thumbnail in the User toolbar for that person.
The next time you have an image that the system did not provide a face box for (or if you just want to manually do so), click the person, resize/move the box over the face and voila... the system will now assign the person to the image. You can do this with as many folks you would like... I find it a bit easier and faster than creating a box and hitting F2 to choose the person... just click, drag and done!
Enjoy!!