Leander Kahney gushes about the little things that are so well designed in Mac software. I agree in the sense that it's small things you'd have never thought of that clinch software. I disagree that this can be applied to all Mac software; I am just now coming back from a session with ProTools, powerful software to be sure, but filled with lots of hidden menus, features, and quirks.
Nothing makes me happy like good software, especially in the moments when it's obvious that something I want to do has really had some thought applied to it. Printing in gmail, for example. Multiple tabs in Firefox. The ! shortcuts for searching in yahoo. iTunes burning an audio file that's too big across multiple CDs. Oh, and the smart playlists on iTunes too. I should make a list someday...