I just noticed a bug in Apple's Backup. When I logging to my laptop, I get a message that states that my iDisk is full. When I looked to see what was filling up my iDisk, I found that it was a bunch of incremental backup files from Backup.
It looks like when you create a backup config, Backup will perform incremental backups of those files. When those files change often, Backup will essentially create full backups daily. This is not a problem, except there is no way to limit the size for one of these backup configuration. In addition to that, there is no way to delete the backup files from within Backup. You have to delete them from the mounted iDisk itself.