
My PC has a stack of 3x1TB HDD's and a single 2TB drive, out of these one drive is only for torrenting and runs all the time irrespective of other stuff running on the pc.
I have a slow 1mbps or 125 KB/s connection but with no bandwidth limitations.
My PC is always on because it is busy processing satellite images on another drive so therefore the torrenting goes on side by side. The only time my PC is shut down is when I am either cleaning it on a monthly basis or the net itself is down.