Right now, saving to iCloud or to the Mac is an option, but it looks to me like Apple really hopes to push iCloud saves as the default. I imagine many self-respecting tech geeks will be annoyed by that prospect -- oh, the Geek Rage will flow! -- as this step is yet another in Apple's War on the File System As We Know It. For everybody else, though, this will be a life- and time-saver. Having your documents always available no matter which device you're using, via a user-friendly interface, will be more important than the inability to directly traverse a file-system; if a computer is lost/stolen/crashes, documents saved to iCloud will remain secure and safe. Yes, other services like Dropbox already do this, but the tight integration with Mountain Lion will encourage its use, and the 100 million+ users already on iCloud illustrate its potential reach.
More iOS bits arrive
Mountain Lion gets other specific iOS app equivalents that are already designed with iCloud syncing in mind. Specifically, to-do's and reminders have been separated from Mail into the new Reminders application; data entered or removed automatically is transferred across devices. Notes gets a similar treatment; and Messages picks up the iCloud sync, too, implemented in ways that solve the problems inherent with Messages' original siloed nature regarding multiple devices.
For instance, do you ever get a message on your phone and wish you could reply from the computer you're on? With Messages, you'll be able to do just that. Messages works on the Mac just as it does on iOS, by using Apple's servers to relay encrypted texts, images, or movies while avoiding SMS rates on mobile devices. Every message is synced across your devices, so you no longer have to be on a specific device for a chat conversation.
Already available on iPod touch, iPhone and iPad, Messages replaces iChat on the Mac, and the main chat window sports a chat interface taken directly from the iPad Messages app. The new interface takes up more screen real-estate than iChat, which is annoying, but Messages gains FaceTime integration, which is not. And the fact that all messages are synced across devices is convenient. You can began a conversation on your desktop Mac, then later take part in the same conversation using Siri on an iPhone.
The mantra is pretty simple: from any device, to any device.
iOS 5 brought to Apple's mobile devices the Notification Center. In Mountain Lion, Mac users play a bit of catch-up with the addition of system-wide notifications. As in iOS, notifications slide out from the menu bar as banners that fade away or as dialogue boxes you must interact with to dismiss; unlike iOS, the notifications on the Mac are justified to the right of the screen. A notification banner will appear for five seconds before sliding off of the screen, exit stage right. The Notification menu icon now resides where the Spotlight icon used to be; Spotlight moves a space to the left in the menubar.
Pressing the Notification button causes the desktop and on-screen windows to shift to the left, revealing the Notification Center. Notifications appear as a list organized by application on the gray linen background made familiar by iOS, and the notification menu icon has a blue in the center when there are new alerts.
The Notifications window slides out from the right side of the screen.
Other than that menu icon, which is unique to Mountain Lion, the entire interface is lifted pretty much wholesale from iOS. The interesting bit is that the interactive elements of Notification Center in OS X feels better on the Mac than on smaller screen devices. Why? Because the elements in Notification Center are perfectly sized for mouse clicks; sometimes it takes me a couple of taps to engage the same widgets in Notification Center on an iOS device.