Sorry, i'm a bit clueless as to the workings of webdav. When I work on a document saved to iDisk, is it better to download it to my local drive or is there no problem with just working directly on the iDisk?
If you are using Panther you can create a local copy of your iDisk and work from that with no problems. When you are online it will sync with iDisk. I do it all the time now.
If you're using another version of the OS you can still work directly from iDisk if you're online but it can be very slow depending on the size of your file and speed of your connection. Having a local copy of everything is a good idea.