I’m just thinking out loud. I don’t have any leaked document or any source at Apple who has told me anything about iCloud.
iCloud will be a service that will be at system level automatically syncing your media assets to itself and to all of your Macs, iPhones, and iPads. Once you check off your photographs, movies, music, documents, etc. to be synced to iCloud it will disappear into the background never to be seen again until you summon it.
I often go to Starbucks and more than not I like the music selection. It’s really easy to find out what music is playing (just look at the Sony monitors or check the iTunes app on your iPhone). If you decide to download music to your iPhone, iCloud would then make sure you have access to that song from any Mac or other iDevice. You’ll also have a web-based iCloud interface to that piece of music as well.
I think syncing services like EverNote and DropBox will have a helluva time trying to compete with iCloud, especially if Apple prices the service aggressively, more aggressively than it has for the very unsuccessful MobileMe. I’m looking forward to what Apple has to offer with iCloud, and at the very best I expect iCloud to disappear once I activate it and all will be as it should have been from the very beginning, from when the first iPhone was introduced.