Daniel Jalkut recently blogged about building your own damn HIG, where he takes inspiration from John Gruber's C4 speech on why the Human Interface Guidelines may be dead. If you haven't read it yet, you may want to so so now.
One thing he overlooks is that, just maybe, computers have become more sophisticated: Back when the Macintosh came out, resource limits forced elements on screen to be simple. Now that we have more colors and more pixels, and bigger hard disks, there's room for more variation, without making things too difficult to recognize.
Similarly, back then Apple pretty much had to introduce people to the GUI. "educate" the users. Nobody knew insertion marks, pointers, the mouse, menus... These days most people are familiar with the basics. Just like a caveman would probably not have understood what a button was before the invention, the race as a whole had to learn, so to say. What would be an odd, stuck pebble, maybe, that you can push a button and cause something else to happen, maybe miles away, is a more recent invention.
That you can move a mouse and a pointer will move synchronously on the screen, and that the "world" on the screen basically works the same as the real world, is even more recent. But these days, children see their parents use a computer, and much of a computer's chips and usability has partially made it into simpler devices, be it the iPod or your TV or your cable box.
I also think that he's overlooking a third option, apart from ignoring the HIG or just following your stomach: Doing your own usability research and creating your own UI, inspired by the basic conventions of the platform you're on (not applicable items are shown dimmed, close boxes have an "X" symbol and either a certain shape or color...).
I often recommend the book GUI Bloopers by Jeff Johnson to people who don't know about usability. Why? Because even though it mainly has screen shots from Windows 95 and System 7, it is still perfectly applicable to today's user interfaces. With the vocabulary of these simpler operating system user interfaces, with these prototypical, I might even say archetypical graphics as examples, it shows you the thought behind the guidelines, not the word up front.
It's like the Bible: "An eye for an eye" doesn't mean: If someone hits you, hit back. Rather, it tells you to consider commensurability: If someone pokes out your eye, don't kill his family as it happened in those days. So, what seems to be a very violent command to today's audience, was actually an obvious call for moderation in the context of ages past.
And before I go off on a tangent, I'd better close this posting.