The iCloud Control Panel is required to use Photo Stream, Mail, Contacts and Calendars (Microsoft Outlook 2007 or later required) and Bookmarks (Safari 5.1.1 or Internet Explorer 8 or later required). 

Note: To create an iCloud account you need an iPhone, iPad or iPod touch with iOS 5, or a Mac with OS X Lion v10.7.2 or later.

Learn more at apple.com/icloud