This is pretty much the practice in telecom. The reason is that metals corrode when more positive than surrounding electrolytes and plate when more negative. Positive ground simply reduces corrosion of exposed wire and connectors. Metal gas pipelines often have high current power supplies to maintain a negative charge on the pipeline relative to ground so they last longer. In automotive environments, the tadeoff is corroding the wiring or the chassis. My guess is that positive ground was abandoned because the metallic chassis connections end up being harder to maintain than the insulated wire connections so it was more favorable to make the chassis more negative.
In my experience (industrial vehicles - 12VDC)
Positive grounding is where the positive is tied to ground and the negative is the supply. Certainly, this is only used in isolated systems.
buzzp -- my experience was in early passenger vehicles which used 6v positive ground (chassis connected to positive battery terminal) -- gave me fits as a kid trying to hook up a 12v 8 track tape player to a 6v 1950 flathead Ford...
nexlink: looks like some additional details would help in answering your question...
