This Windows 2000 article provides some interesting insight into Microsoft's reaction to Mac OS X:
However, sources close to Microsoft told me that the company's programmers are having "panic attacks" about Mac OS X's new Aqua UI. Particularly troubling to Microsoft is Macintosh's new intuitive Finder (i.e., the Mac version of the Windows Explorer shell), which features several panes that simplify drilling down through subdirectories. Microsoft's UI team is suddenly playing catch-up-with-the-Mac again, and we probably won't see the fruits of their labors until Blackcomb arrives.
"Blackcomb" is the next, next generation of Windows due in 2002-3.