The iDisk feature of .Mac can be very useful, however it seems to be plauged by slow speeds (I find it impossible to use without the local iDisk turned on) and sync issues (automatic sync causes corrupted files in some apps). Even with auto-syncing off, open/save dialogs and even opening Finder windows can cause a spinning rainbow cursor; sometimes for over a minute.
The problem lies in the fact that the local iDisk (stored in /Volumes/iDisk) has symbolic links (aliases) to folders on the remote iDisk (/Volumes/your_mac.com_name). When OS X lists the local iDisk's contents, info for these folders must be loaded from the remote iDisk, which can take some time. The Open and Save dialogs are particularly bad if they default to a location on the local iDisk, because the column view that displays the files and folders includes the alias folders at the root of the local iDisk.
As some people have noted, the problem gets better after the first incident. This is because OS X is kind enough to cache the remote folder info. However, I have found that the problem can persist and present itself in various ways.
I offer the following shell script that works for me to solve the problem. It unlocks the local aliases (Backup, Groups, Library, and Software), sets them as invisible, and then relocks them. Since the aliased folders are now invisible, OS X no longer tries to load info for them when displaying open/save dialogs or local iDisk folders in the Finder. There are a few caveats with this tip:
#!/bin/sh
linkedfolders=(Backup Groups Library Software)
for folder in ${linkedfolders[@]}; do
/Developer/Tools/SetFile -P -a l /Volumes/iDisk/$folder
/Developer/Tools/SetFile -P -a V /Volumes/iDisk/$folder
/Developer/Tools/SetFile -P -a L /Volumes/iDisk/$folder
done
exit 0
[robg adds: I have not tested this one. Remember to make the script executable (chmod a+x script_name). Note that you should be able to reach the hidden folders from the Finder using Go -> Go to Folder, and entering the full path -- /Volumes/iDisk/Backups, for instance.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060509114042920