I have to say, I really don’t like the direction the OSX interface is going. All this flatness is tremendously boring. I’ve found myself very nostalgic of the old ”Aqua” interface several times in the last few months.
Unfortunately, Jony Ive’s iron grip is so tight, all theming/customization hooks have been removed from recent OSX releases. There is now no application (that I know of) which could reskin windows, toolbars and scrollbars.
The only avenue left to UI tinkerers is icons. You can still use LiteIcon to override system icons, and of course copy-paste on individual folders. I’m currently using icons from the classic Iconfactory World of Aqua series, and I just love them.
Some programs will thankfully allow you to customize them. There are plenty of Aqua themes for Firefox, I use a slightly cheesy one. iTerm2 has an ”Aqua” option for its tabs.
If you are an app developer — please consider some skinning support. For all the talk about ”consistency” from UI nazis, the first thing people do on a new computer is still to customize the desktop background...