As a faithful Apple customer with a MobileMe account, my first thought was to use my iDisk to transfer files. I put files into my "Public" folder, then on the server in the Finder I choose Go > iDisk > Other User's Public Folder. The Finder mounts the public folder as a drive. Works well. Until it doesn't.
Twice now I've been burned in Mac OS X 10.6.4 and .5 where the Finder gets confused about the mounted iDisk folder. One symptom of this Finder bug is refusing to dismount. The Finder complains that a file is in use, but that's not true. The list of files in the mounted iDisk no longer updates its display to show current contents. "Force ejecting" the mounted iDisk fails. Your only option left is to force-quit the Finder. But that hoses your Mac, requiring a restart of your secure server. That's a drag.
I don't expect a fix soon. The Finder has always been lousy with bugs related to iDisk and its WebDAV protocol. With Snow Leopard, the Finder got a re-write in Cocoa from Carbon, which means new hiding places for bugs.
One dead-simple workaround:
Rather than mount the iDisk in the Finder, use a web browser.
Apple has been greatly improving the web access to MobileMe features. That includes iDisk file access. A nice multi-columned view of the file system appears in your web browser when you access the iDisk icon.
To log in to your MobileMe account with full access:
To access somebody's iDisk public folder, point your web browser to:
By the way, there are some other handy such URLs for accessing a MobileMe account's picture gallery, calendars, and web site.
You may be able to use Safari or other web browsers such as Camino, Firefox, Chrome, or Opera. I've some of those successfully, but don't recall which. You may get a warning message, but I've ignored it with no penalty.