Apple Inc. has posted the following FAQ:

What’s happening to MobileMe?
Effective June 6, 2011, if you had an active MobileMe account, your service has been automatically extended through June 30, 2012, at no additional charge. After this, the MobileMe service will no longer be available.

What will happen to the content I have on MobileMe?
Apple has announced a new service called iCloud which will be available this fall and free for iOS 5 and OS X Lion users. When you sign up for iCloud, you’ll be able to keep your me.com or mac.com email address and move your MobileMe mail, contacts, calendars, and bookmarks to the new service.

When iCloud becomes available this fall, more details and instructions will be provided on how to make the move.

Can I create a new MobileMe account?
You can no longer create a new 60-day trial account or start a new subscription using a code contained in a MobileMe box. However, if you have a Family Pack subscription, you can still create new family member accounts.

Can I upgrade to a Family Pack or purchase additional storage?
Effective June 6, 2011, you can no longer upgrade your Individual account to a Family Pack or purchase additional storage for your MobileMe account.

I purchased a MobileMe box and have not used the activation code inside. Can I get refund for it?
Yes. If you have an unused activation code from a MobileMe box, you can submit a refund request. More info here.