I'd have to disagree. I've been uploading stuff onto iDisk at 1Mb/s+ (downloading at 2Mb/s the other day) from school and at least 100+kbps (170kbps downloading) from home.
It's very fast...
Interesting... Do you use Leopard, as I do? I've heard the iDisk is faster in Tiger.
By the way, I can upload to Amazon S3 at 400KBps, which is the maximum bandwidth my connection allows.