Preview at WWDC likely in June, followed by September launch.
Apple Gives Additional Year of Increased iCloud Storage to Former MobileMe Members
When you moved your MobileMe account to iCloud, we provided you with a complimentary storage upgrade beyond the standard 5GB that comes with an iCloud account to help you with the transition. Originally, this storage upgrade was set to expire on September 30, 2012.Apple notes that users received either 10 GB, 20 GB, or 50 GB of additional storage -- on top of iCloud's standard 5 GB -- depending on the amount of MobileMe storage the user was paying for when the service transitioned to iCloud.
As a thank you to our former MobileMe members, we will continue to provide you with this complimentary storage upgrade at no charge, for an additional year, until September 30, 2013. No action is required on your part. For complete details, please read this article.
Thank you again for using iCloud,