Apple appears to be testing a notification service on the iCloud website. The test message appears at the top of the browser window upon logging into iCloud.com.
Apple introduced a new notification system in iOS 5 and has announced that a similar feature will be coming to the Mac in the Mountain Lion operating system this summer.
It's possible that Apple will include syncing code in iCloud to share notifications across devices, for calendar alerts and new mail, or the notifications may be used for some other purpose.
Article Link: Apple Testing Notifications on iCloud Website