Simon:
The idea (and reason) is I downloaded the RedHat 7.2 ISO's down an ISDN line and it took 3 days (including 2 disconnects that I didn't pick up on)...
Yes, getting some shared ISOs is probably useful, although I wish more distributions would follow Debian's lead of starting PPP network installations from nothing more than a few floppies and some hard disk files. They're taking it even further in the next version and letting you download the hard disk files after the installation has started, I believe. Why on earth would anyone want to download 600Mb and only use around 200Mb of it?
So, the answer's simple: use Debian! ;-)