also, aluminium cases are nice. But they act as boxes, and you have to pick your z out of them. When I bought my sl-c860, I bought an aluminium case, cause I thought it was cool, thin, tough and a lot better of those ugly PDAir cases.
Now I have a PDAir leather case, and I don't use aluminium case anymore. As to speed, PDair leather cases are umbeatable; you can take the CF card inserted, and you have not to thorow them away when using the zaurus.
On the other hand, you have a Sharp Big Mac instead of a Sharp Mac Toast.