If you had said "how big is a good size human bone??" then I would have laughed........
size is a measure of perspective. Depends what you want and what you need......please don't construe this sexually, but if you do, hehe. But in terms of a harddrive, one might say that 60-80 gigs is large because it is available on most newer model computers (don't quote me....its close to that) In society most people know what to consider to be "big"...all you need is a reference point to start with.