And like you say, a lot is simply good design. Apple didn't invent nearly as much as their marketing department (and legal) would have us believe.
Tangentially, I've fallen in love with tiling WMs, but they all seem mediocre at best. @aroman it'd be awesome if you guys made an alternative tiling WM that was as sleek as your windowing manager.
I still switch to Windows occasionally for gaming (although I try to limit my gaming habit). Another reason for using Windows for me would be screen capture software (Webcammax [best], Manycam, more...) which is completely absent from Linux (hint hint, elementary. I think this could be revolutionary).
I like:
1) tile movement is very dynamic; it's tree-based
2) supports transparent terminals; I like seeing my pretty wallpaper
3) mod key works well for switching desktops, and moving tiles between desktops
4) good multi-monitor support.
I don't like:
1) no dropdown application menu. dmenu is ok, but I need to find a good menu bar app.
2) You can mouse drag-resize, but not drag-reorder tiles. It's on their todo list.