iCloud services are tied into apps like Mail, iCal and Address Book. But you can also access your data through the iCloud.com web site. This allows you to get your email and access your events and contacts even when you are using a computer that doesn't have iCloud. The web-based apps are very sophisticated, offering almost the same functionality as the full apps, and often more functionality than the iOS apps. You can also use iCloud.com to transfer documents between your Mac and iOS devices, even in Lion.