As far as I can tell, on my van which is negative-grounded, all fuses are somewhere between the positive terminal and the load being protected by the fuse.
However, some switches are on the positive, some on the negative side. For example:
The ignition switch switches the positive.
The sliding door switch switches the negative. This controls the light in the load bay, which is otherwise un-switched directly to the battery's positive via a fuse.
I'd have thought the positive should ideally be switched, since otherwise if a mechanic or user assumes there is no potential around the switched item while it is off, he would be wrong if it is ground switched. (The wires to the load still have positive potential with respect to the chassis).
What reasons might there be for negative connected switches?
I can give more info if required. (I'm following the Haynes manual which has pages and pages of circuits. I'm not entirely sure what's relevant for this question)