An idea which has been creeping up on me from the side over the last couple of weeks hit me square in the face today. No matter what standards we Cocoa types use to create our user interfaces, the official Aqua HIG, the seemingly-defunct IndieHIG, or whatever, ultimately producing what is considered a usable (or humane, if you like) interface for Mac OS X is not only difficult, but certainly unrepeatable over time.
The "interface" part of a Cocoa user interface is already hard enough to define, being a mash-up of sorts, and to differing degrees, between the Platinum HIG which directs the default behaviour of some of the *Manager controls and the OpenStep HIG which describes the default behaviour of most, if not all, of the AppKit controls. If that isn't enough, there is an inexact intersection - some controls work differently in (what are loosely called, and I'm not getting into the debate) Cocoa apps than in Carbon apps. There have also been innovative additions on top of the aforementioned guides, such as sheets, unified toolbars and (the already legacy) textured interfaces. There have been subtractions from both - miniwindows still exist but nobody uses 'em, and window shading went west with Rhapsody.
But all of that is related to the user interface, not to user interaction (I'm in the middle of reading Cooper's The Inmates Are Running the Asylum, I'm going to borrow some terminology but studiously avoid discussing any of the conclusions he presents until I'm done reading it). It's possible to make HIG-compliant inspectors, or HIG-compliant master-detail views, or HIG-compliant browser views and so on. It's also possible to make non-compliant but entirely Mac HID views, coverflow views, sidebars and so on. But which is correct? Well, whichever people want to use. But how do you know which people want to use? Well, you could get them to use them, but as that's typically left until the beta phase you could ask usability gurus instead. Or you could take the reference implementation approach - what would Apple (or Omni, or Red Sweater, or whoever) do?
Well, what Apple would do can, I think, be summed up thus: Apple will continue doing whatever Apple were previously doing, until the Master User takes an interest in the project, then they do whatever the Master User currently thinks is the pinnacle of interaction design. The Master User acts a little like an eXtreme Programming user proxy, only with less frequent synchronisation, and without actually consulting with any of the other 26M users. The Master User is like a reference for userkind, if it all works for the Master User then at least it all works for one user, so everyone else will find it consistent, and if they don't find it painful they should enjoy that. The official job title of the Master User role is Steve.
All of this means that even inside Apple, the "ideal" usability experience is only sporadically visited, changes every time you ask and doesn't follow any obvious trend such as would be gained by normalisation over the 26M users. Maybe one day, the Master User likes inspectors. Then another day he likes multi-paned, MDI-esque interaction. On a third day he likes master-detail control, in fact so much so that he doesn't want to leave the application even when it's time to do unrelated work. Of course you don't rewrite every application on each day, so only the ones that he actually sees get the modernisation treatment.
So now we come back to the obvious, and also dangerous, usability tactics which are so prevalent on the Windows platform, and one which I consciously abhor but subconsciously employ all the time: "I'm the developer, so I'll do it my way". Luckily there are usability, QA and other rational people around to point out that I'm talking shite most of the time, but the reasoning goes like this. I'm a Mac user, and have been for a long time. In fact, I might know more about how this platform works than anyone within a couple of miles of here, therefore(?) I know what makes a good application. One problem which affects my personal decisions when trying to control the usability is that I'm only tangentially a Mac person, I'm really a very young NeXTStep person who just keeps current with software and hardware updates. That means I have a tendency to inspector my way out of any problem, and to eschew custom views and Core Animation in favour of "HIG is king" standard controls, even when other applications don't. And the great thing is that due to Moving Target reference implementation, I can find an application which does something "my" way, if that will lend credence to my irrational interface.
The trick is simply to observe that taking pride in your work and expressing humility at your capabilities are not mutually exclusive. If tens of other Mac users are telling me they don't like the way it works, and I'm saying it's right, apply Occam's razor.
And if there isn't enough fun for you in one usability experience, a bunch of us are presumably going to be providing the iPhone HIG-compliant V on top of our Ms and Cs before long.