Apple just updated the .Mac, as well as the version of Backup. I have just run the new version of Backup, and I like the the changes that they made.
Now Backup 3, has backup plans for more types of files, like purchased music, and other iLife files. Also now when you backup files to your iDisk, Backup creates a local disk image, and then it copies the files to this mounted disk image. Then it compresses the image, and uploads this to your iDisk.
This improves the time that backup takes, as it only has to copy one compressed file, instead of tons of uncompressed files. The one downside of this mechanism is that if the disk image gets corrupt on the iDisk, most likely all of the files will be unrecoverable.