I don't think anyone actually shaves them off? Aside from a few very 'eccentric' individuals. Most girls just pluck then neaten out the shape with pencil... Granted a lot do this to excess and they end up looking like they're entirely pencilled on.
Here in the Middle East, I've seen several Arab women who have shaved off their eyebrows and they draw it on everyday. But I still never understood why they do this!
The only girl I know who actively shaves them off entirely does it so she can use liquid eyeliner to draw thin lines to match her hair which is generally an unnatural neon colour.