A couple of new things added.
First, the 20MB of online space are free to any mac user (OS 9 or later). If you pay something like $1US per MB you can get up to 1GB of space. In addition, there's no ads anywhere, especially no Pop-up ads. No upload/download limits AFAIK, and great speed, over the Akamai backbone. Plus, there's links to software updates for download. You can mount it onto your desktop and save and execute stuff off of it. Sorta like a substitute for a floppy disk, great for iMacs and classwork.
in addition, Apple recently upgraded the iDisk with Mac OS X 10.1 so that it can connect using Appleshare AFP, or now using WebDAV so it can go around firewalls as well as stay connected indefinately to the mounted iDisk.
Even better, the WebDAV makes it cross-platform to any WebDAV client. In Microsoft Word, if you save into a web folder, give the web folder address as http://idisk.mac.com/username and give username and password to access the drive.
For older clients, like Mac OS 8, open the chooser. Click appleshare, then server. Type in idisk.mac.com After that it will ask you for a name and password, use the ones supplied by iTools or your mac.com name and password. From there it mounts the volume on your desktop, like a virtual floppy.