Apple has started seeding OS X Lion 10.7.2 to developers, which unlike previous versions, includes built-in support for iCloud. The build number is 11C55, and if your an Apple developer, you know what to do.
OS X Lion Software Update 10.7.2 is an update to OS X Lion 10.7 and includes support for iCloud beta. Please refer to the seed note for more details and installation instructions. (Mac Developer Program membership is required)