I have been away and have just returned to find all your answers. Thank you, one and all. I hope that my questions haven't caused a diplomatic incident! The following questions remain unanswered, so I'll try and answer them myself, and hope that someone will correct me if I am wrong:
Does one have a different share ratio for each file downloaded/uploaded?
Is it acceptable practice to take files out of my shared folder once I have a 'reasonable' share ratio?
I guess the answer to both questions is 'yes' and that a reasonable share ratio, defined as UL/DL, must be at least 1.
Nick