Well, protectors such as the
G2 or
NuShield slip between the screen and the case. Since they fill the already small gap, this probably helps to prevent dust from sneaking in that way. There were other ways for dust to get inside older Pocket PCs, but I think those problems have been resolved in the current generation. (Dust used to be able to enter through the stylus slot or CF slot, as well as the gap around the screen, but I think all displays are sealed these days to prevent stuff like that from getting inside the display.)
--
Dave