Apple has updated Backup (http://support.apple.com/kb/HT3991), a MobileMe component, to version 3.2. It’s recommended for all users of Backup 3.
According to Apple, this update improves the overall reliability of Backup and uses space more efficiently on your iDisk or local storage by automatically recycling older backup data. When backing up to iDisk, older backups are recycled every 30 days for daily backup plans and every 12 weeks for weekly backup plans.
For example, if you are backing up to your iDisk on a daily basis, Backup will maintain a minimum of 30 days of backup history. You may choose not to recycle when backing up to a hard disk, CD, or DVD, but recycling is recommended as it uses storage space more efficiently and improves reliability when restoring your data, says Apple.