My view of Themes
I can see both sides of the unlimited-theming question. It's fun to make it easy for anyone to install any theme. At the same time, it makes Macs harder to use for newcomers--the confusion of going from Mac to Mac. And it destroys a very important part of Apple's brand identity, making OS X impossible to spot when it's in use. I think Apple probably ought to limit theming--but leave an unofficial back door for expert users to do it anyway. Just like OS X has now. I'd love to make my own themes!
Here's a thought on themes Apple could offer to preserve the OS X identity, yet still allow lots of individuality:
* Textured Glass (just like now)
* Smooth Glass (remove the stripes--and the brush-texture on the metal--but keep the metal gradient/shine)
* All Glass (just like now, with the metal apps turned to a smooth/stripeless glass, with the thickness along the edges and the rounding still there to distinguish these apps)
* All Metal (everything brushed metal, and the current "metal" apps being distinguished by the thickness/rounding)
* Black Glass (like now, in black plus the widget color; menu and title text in white)
* All Black (like now without any metal, in black plus widget color)
* Have Large (50% bigger for tight-DPI screens) and Small (like now) variants of each. The mouse pointer would be bigger too.
* Let the Dock background be Light, Dark, or Invisible.
* Have several colors for the widgets: Graphite, Blue, Violet, Sage, Ruby, Amber.
* Have a Hue Wheel and Saturation slider (no value, that would conflict with brighness changes needed by the UI) for mixing custom widget colors. It could simply custom-shift and re-save fresh versions of all colored widget graphics, like you could do in Photoshop. (No need to process the colors on the fly if they are all done at the start.)
* Make folder icons tint slightly in the direction of the widget color--instead of always being slightly blue. (But Label colors would be much stronger colors, always easily spotted.)
* Include a set of desktops to match each standard widget color.
* Allow a choice of login backdrop.
* Have two choices for the window stoplight widgets: Always Colored (Red-Yel-Grn) or Only Colored on Mouseover. (The second option would make them match the other widgets most of the time. But even Graphite could benefit from tri-colored widgets when you mouse over.)
My view of what the guidlines for metal/textured ought to be: if you create documents--a productivity app with the usual File menu being used all the time--then keep it white like the Finder. For non-creation apps (utilities, players, "desk accessories" etc.) use metal. That's the pattern I see so far--if Sherlock goes back to metal. (And Apple was never rumored to make Panther all metal, just make all their little apps metal. Which fits my thinking.)
And I like the two looks together, personally.
I actually like the flatter look of Jaguar, and I expect Panther will go one step further, adopting the look of Safari's buttons (as far as the shine). They are still clear and 3D, and I like the new look.
As for sounds--I want my Howler Monkeys back!