Most people with jointers have discovered that they don't want to edgejoint plywood. The plywood edge dulls the knives very quickly. The usual explanation for this is that the glue line eats the knives; few of us seem to think that wood could be responsible.
I got curious. I had a set of knicked knives, so I ran the obvious experiment. I set the fence in one location and ran plywood until I could clearly see the wear on the knives. The wear was not at the glue lines, but rather at the end-grain plies. That is, it is the end-grain wood which dulls the knives so quickly!