Many people have posted saying that they have a tiny camber, or they think (or hope) that the center of their blade is flat---they just nip off the corners. This suggests a method where you really wish your blade to be straight, but you need a little camber to prevent those nasty tracks from the corners.
But this type of camber is not going to help much with stock preparation as described in Charlesworth's DVDs. In that method, the whole point of the camber is that you can take a shaving that is markedly thicker on one side than the other. This gives a method for correcting an edge that is not square. But a teeny tiny camber won't do because it doesn't give a sufficiently uneven shaving---you'll plane your whole board away trying to get it square. If you want to work this way then you need the camber of 0.25 mm at the ends which in my experience is a pretty big camber, and it seems to require removing a significant amount of material. This amount of curvature could be larger than my microbevel, so I do not agree with the person who said the camber is applied "only during honing". I see this as part of the shaping of the edge. I find it takes an eternity to install such a camber with my 1000 grit stone. I go to coarser grits.
What is worse is that if you have a plane with a low bedding angle then the camber required to get the same cutting effect becomes much larger. So if you want to prepare a low angle plane with a 12 degree bed angle to cut equivalently you need a camber of 0.85 mm at the edges. I have used a powered grinder....
Regarding the shooting board, Charlesworth himself says that the 0.25 mm camber doesn't bother him with the shooting board. But as others have noted, if you're worried about it you can get a second blade for shooting. I personally never produced a square edge until I cambered my blade and used the Charlesworth method.
