Scott,
The scrub plane does just that to the wood, scrubs off the excess. It's not intended to give anywhere close to a final surface, only to get rid of the bulk material. If you look at the back of old boards in furniture or floors you can often see the wide, shallow grooves cut by the scrub plane. These grooves usually run across the board at an angle, not along the length of the board. When doing a board, you then level it off the finished side with a standard plane. The scrub plane has a lot of advantages over a draw knife for basic shaping of a stock as it doesn't have that nasty tendency to split off pieces. You can, however, get pretty close to a final surface by having just a bit of the blade extended.
Tom