Don't forget speed...although not really a problem on iPods...
Actually, hard drives do better for speed on larger transfers - on small random reads/writes, flash is better because there's no head movement or rotational latency.
For example, Windows Vista can use a USB flash drive as an I/O accelerator: ( http://en.wikipedia.org/wiki/ReadyBoost )
quote:
"Using ReadyBoost-capable flash memory devices for caching allows Windows Vista to service random disk reads with performance that is typically 80-100 times faster than random reads from traditional hard drives. This caching is applied to all disk content, not just the page file or system DLLs.
Flash devices are typically slower than the hard drive for sequential I/O, so to maximize performance, ReadyBoost includes logic to recognize large, sequential read requests and then allows these requests to be serviced by the hard drive."
Flash devices are typically slower than the hard drive for sequential I/O, so to maximize performance, ReadyBoost includes logic to recognize large, sequential read requests and then allows these requests to be serviced by the hard drive."