I've been using the "Seal Savers" for several months now and I'm very satisfied with them. They look great, are cheap and keep the seals clean, although I do clean them out after each ride with the air hose. Since I ride in the desert, the will build up a little sand just inside the top portion of the cover, so I fold them over and blow them out. I don't know how they would work in an area where they would get wet, or how they would hold out mud.
I've also heard that forks without the large rubber boots will let a little more air to the radiator, but don't know if it's true or not. So far though, I like them.