People are worried about the cloud-killing PR mistake or security breach that will cripple the efforts to get data into these controlled data centers, so this makes perfect sense. Start the focus with something everyone will know: Music. If someone breaks into your music collection... oh no? I was keeping my Duran Duran passion a secret.
Once this catches on, any mistake won't be a crippling one or a business-critical error, just a little frustrating. Gradually promote the other cloud offerings afterward, even if they have been there the whole time. Tied in with Lion's auto-versioning options, this just means everything naturally goes to the cloud, and no one will ever think of it again.
As stated, this isn't to kill Windows, this is to kill the pain of buying more devices. This is the first step to build that confidence and show it off in something people will have fun with.