From one perspective, Jobs and Raskin ended up going down two opposite paths.

Raskin emphasized that "modes" were a major cause of UI problems. Essentially you want a UI that the user can habituate to as strongly as possible, so that all one's attention can be focused on the actual task and all of the administrivia you need to do tell the computer your intention are handled subconsciously. Like touch typing at a higher level.

The issue with modes is that they break habituation. If performing a given UI gesture does one thing in one mode and another thing in another mode, you can't make that gesture a habit. For example: Cmd+Z is a conventional gesture that many applications interpret as undo. If the keyboard shortcut changed between applications (or worse Cmd+Z meant something else in another application/mode), it wouldn't be so habitual and you'd be less productive.

Raskin was very serious about no modes. The Cat for example didn't even have an on/off mode. It would go to sleep to save power, but if you started typing it would buffer all your key strokes and have them in your document by the time the thing woke up. That is, you didn't have to switch from off mode to on mode! And because you were always in a document (that is, there were no separate application modes), you knew that typing some words always did the same thing, so the scheme really worked.

On the other hand, Apple has really pushed, especially since iOS, on the "App" model. Applications are, of course, giant modes. And the strategy has been to push a separate App (mode) for every single use of the machine. So rather than learning a few powerful gestures and then combining them to do disparate tasks, users need to learn a separate, surface-level gesture complex (App) for each individual task they want to do on their machine.

Which is more efficient or appealing? On what time scale of use?

Did Apple end up this way because Apps are a more natural fit for a consumerist model? "Want to do this task with your machine? Don't bother figuring out how you can do it yourself. There's an App for that!" No Modes vs Buy More Modes?

Raskin's book, The Humane Interface, talks extensively about his UI design philosophy. In addition to explaining the above problems with modes, he discusses how to actually design a computer system with no modes (I believe an elaboration of what he did with the Cat). He also explains other really important UI principles and their ramifications, for example, "The user's data is sacred" (hence undo).

PS:

Raskin's definitions: A gesture is defined as an action that can be done automatically by the body as soon as the brain "gives the command". So Cmd+Z is a gesture, as is typing the word "brain". What constitutes a single gesture will be different depending on the user! A mode is defined as any situation not at the user's locus of attention that would cause a gesture to perform an action different from another mode. So "pseudomodes" where the user holds down a modifier key or holds the mouse button while performing a drag gesture get around this since they keep the user's locus of attention on the fact that they are performing the pseudomode.

I think both the above definitions are still a bit problematic but Raskin's definitions are better than any other that I've heard. I hope there are more people who study and discuss these deep UI design issues! What do you think about modes?