John Gruber discusses some niceties of the Mac UI:
For example, I recently discovered that if there are two or more files sharing the same name in the Open Recent menu, Mac OS X also shows where do they come from – a very nice touch.The pixel clicks are indeed nifty. That inspired me to see what happens when I option-click the green 'window grow' icon. My window pops over to the top left of the display. Nice surprise.
It’s not recent, but the most delightful surprise I can remember from the last few years is when I discovered that you can use Command-Tab switching when you’re in the middle of a drag. So you can start dragging something in one app, then use Command-Tab to switch to another app, and then complete the drop in the new app. I don’t even know when this happened – it might have been like this on Mac OS X all along, but I don’t think I noticed until sometime during the 10.2 era. This also works with things like Exposé and Dashboard.
It sounds obvious, but doing something like that was completely unheard of on the old Mac OS.
A lot of the stuff I wrote about in my Tiger details report delighted me to some degree. For example, I love that you can now click in the very top-left pixel of the main display to trigger the Apple menu (and likewise for the top-right pixel for the Spotlight pseudo-menu thing). I think the Apple menu should have worked like this all along.