You should avoid plucking above the eyebrow as it goes against the natural shape of it. It makes it difficult to maintain and, I suppose, can maybe make it look 'overdone'.
http://www.orientaldancer.net/articles/eyebrow _design.shtml
How To Shape Your Eyebrows:
To determine exactly where your brow should begin, hold a makeup brush or a pencil straight up and down against one nostril. Where the pencil lands by your brow is where it should begin. The brow should end a little past your eye (if it grows down too far it will drag your eyes down). If you have a natural arch, work with it. If you need to create one, look into your eyes. The arch of your eyebrow should fall directly above the outside of your iris. Using an eyebrow pencil, fill in the brow area that you want to preserve so you can pluck outside the edges.
A. Take a thin make up brush and place it at the side of your nose straight up and down. Where this line ends near the brow, your brow should start from there.
B. Take the same make up brush and angle it from the nose to the pupil while looking straight ahead. Your arch generally peaks where the make up brush meets your brow.
C. Again take the make up brush and angel it from the nose to the outside of the corner of the eye. This is where your brow should end. It should never drag below this area either or it can drag your eyes down.
Hope this helps,
ws x