Currently, Mac users can use either WebDAV (an HTTP-based protocol) or AFP (Apple Filing Protocol, the protocol used by OS 9's File Sharing and OS X's Personal File Sharing) to connect to .Mac iDisks. However, on Wednesday Apple sent out an email to .Mac members noting the imminent discontinuation of AFP support:
"Dear .Mac Member
On December 2, 2003, we will have completed our move to WebDAV as the supported protocol for iDisk access. If you're using Mac OS X, this amounts to a non-event; WebDAV is built into Mac OS X so it's what you're automatically using to interact with your iDisk now. If you're using Mac OS 9 and AFP you'll need to download and install software that enables WebDAV for your operating system in order to maintain full access to your iDisk. Until you've done that, you'll still be able to read and download files from your iDisk using AFP but you won't be able to upload files to it. Open source software called Goliath, available at http://www.webdav.org/goliath/ performs this service and specifically supports iDisk in its File menu. On January 20th, 2004, iDisk will only be available via WebDAV, so we encourage you to make the change from AFP to WebDAV now."
As Apple mentioned, if you're using OS X and normally connect to your iDisk using the Go -> iDisk menu item in the Finder, or via Apple's iDisk Utility, this change will not affect you at all. However, if you use OS 9, or if you currently connect to your iDisk using AFP (many users do for reasons of convenience), this will change the way you need to connect.