Pretty much any time I'm not doing macro photography, taking pictures of the stars, or doing video. Autofocus in modern cameras is faster and more accurate than just about 99% of photographers.
All the time. Pretty much the same as Kerbouchard - macro is the only time I touch the focus ring. (And I still do use AF a lot for that too.)
'Back button' focusing does help too, because whenever you do want to manual focus, all you have to do is not press the AF button. No switches to flip.
Selecting the most appropriate focus point helps a lot too - especially for portraits.
I think the reason for the question could be this: Laurenvictoria, perhaps you are confounding autofocus point selection with autofocus. Often cameras default to automatic focus point selection, i.e., autofocus is done on one of the focus points available, chosen automatically. This is hard to use in portraits but also in other kinds. Set it to be just one fixed point (the central one is ok, but if you do portraits in portrait orientation, it could be as well one of the left/right points). Then you use autofocus but in the point you want. If needed, after having autofocused (half-press), you may recompose your picture.
Whenever I'm using an AF lens. The only time I manually focus is when its too dark for the camera to focus, or when I'm using manual focus lenses. Yeah, I own a couple of those.
Most of my shots are manual focus, because my most used lenses are either manual focus only, or really wide. If I'm taking action shots AND I want a shallow DOF, then I use autofocus.
autofocus? yeah, never heard of it...I have cruise-control as well...may save gas...but I like feeling my foot on the accelerator...powersteering is cool and all...but I'd rather feel the road with manual steering...automatics are great...no better way to get to know your vehicle than when you have to shift manually...