Some third party applications currently use the MobileMe and Sync Services. Once you move to iCloud this will no longer happen unless the developer has prepared for it. If you are a MobileMe member to find out if you have any applications using this service click the Apple () menu and choose System Preferences > MobileMe > Sync. Third-party applications will be listed below Preferences.
If you don't move to iCloud these services will continue until June 30th next year.
Mark Ford 