This was an issue in Jaguar, and still in Panther. Pathetic...
Again, Apple doesn't seem to know what a 56k modem is and they are under the illusion that everyone has 300k/sec upload capability.
I wish that the iDisk was as flexible as KDX in terms of file transfer. KDX will properly upload any type or size of file from any connection to any type of KDX server. And if you don't set iDisk to sync with your hard drive, browsing an iDisk is patetically and unacceptably slow. They should have an option of an iDisk Browser app which leaves out all that extra information such as icons and such. Browsing KDX servers over a modem is completely usable.
Edit: On top of the iDisk being slow, it also ties up the Finder! Again, a widley known issue in Jaguar/Puma is still existing in Panther. I was so shocked to learn that the Finder still hangs when you're loading an iDisk folder in Panther. I thought the "brand new Finder" would fix that. Completely unacceptable.