Brent Simmons (via John Gruber):
How comfortable are you with outsourcing half your app to another company? The answer should be: not at all comfortable.
I used to argue that the value of an app using iCloud for its web back-end was based on the users’ trust of not handing your personal information over to yet another overnight startup to use in whatever way it may. But what the recent shutdown announcement of Google Reader (and the not-so-recent shutdown of iDisk) proved is that big companies are just as fallible to the whims and needs of business as startups (though, perhaps not to the same extent or frequency).
The main advantage that iCloud has is the zero setup configuration — when you launch an app, it provides a dialog for the user to authorize, with one tap, the use of iCloud syncing. But the few additional taps required to set up Dropbox within the app, or to create a new account, are well worth it for most developers to provide the web services they need.