I dunno, I assumed it would be using some power or something, it shows up still.
On a more productive tack, I can take it out physically to reduce weight; is it possible to replace it with a 2nd HDD or even an SSD? Maybe even replace my HDD with a SSD by cloning it across? It's not the fastest Mac but I already upgraded to 4Gb RAM and am just installing 10.8 so thought a SSD might give a new lease of life.