Let me add that Apple and MS often borrow from each other, and I understand to do this is an actual legal agreement between them, stemming from '90s-era lawsuits regarding OS GUI intellectual property.
I believe Apple sued MS for stealing look and feel, but lost as they'd themselves nicked the attributes in question from Xerox PARC.
MS also helped prop up Apple financially when Apple looked like they were going down the tubes, as MS needed the competition to avoid being broken up by the Government. So that may have some bearing on it.
For instance, on the Mac you can app-switch by using Command-Tab. In XP you use Alt-Tab (IIRC). Maybe MS offered that feature first; I'm not sure. Apple's implementation is nicer, though ;-).
Apple borrowed from Windows as much as the other way around, though Apple would never admit it and deliberatly do it differently even if it's less efficient. Though the recent trackpad changes have finally caught up with 5 year old PC ones and surpased them with the more advanced gestures. Still not second button, which is easier than Apple's way of saving face by using 3 fingers rather than 1. I find I have to use the mouse a lot more in OS-X than XP, a lot more. Generally I find Windows has the edge with er window's handling, 4 edges and 3 corners more in fact. Much easier + simpler to deal with.
Alt+tab for switching between apps was used in Windows first [Cntrl+Tab switches between windows in a Window's app]. And I prefer the Windows way as you can Alt+Tab between each iteration of a say Explorer, whereas you have to Cmd+Tab and then switch between windows using Cmd+' to get to separate Finder windows.
I quite like Expose, but I find Cmd+Tab quicker + easier. Expose is for those who can't work out Cmd+Tab, but with fancy graphics.
One thing I like about OS-X's Finder is the column view, which even Vista doesn't seem to have. I hate large icon views and don't like simple lists much either. Columns are easy to navigate quickly using the arrow keys.
Finder is still pathetic and clumsy in so many ways, including the column view. You need an enormous screen size to deal with deeply nested folders and long names. It's the antithesis of what Macs purport to be. Not easy or inutitive, certainly not good, simplistic maybe. I've also asked very basic questions about using Finder in Apple stores and the 'Geniuses' there have no idea how to answer.
Oh and you can navigate Explorer using keys too, though I can't recall quite how as I've not used it for ages.
Finder + iTunes are the two worst programmes I can recall using. Though at least one doesn't have to use iTunes.