System utilities: Apple's system utilities are night and day ahead of Microsoft's. Some examples: The Startup Disk utility lets you boot off any drive easily; try that with Windows. The Sharing system preference makes it much easier to control your Mac's security than Windows' tools do; plus, you get more control in one place with Mac OS X. (And the Secure Delete feature is an easy way to secure deleted files when you empty the trash -- another feature Windows doesn't offer.) The Time Machine software is an incredibly easy, powerful backup utility bundled with the OS that makes Windows 7's look like a holdout from the DOS era. Backup is automatic, sure. But recovery is where Time Machine really shines; just zoom to a past state and select it to go back to that point. If you're in an application, you can restore just that application's state, so changes elsewhere aren’t also rolled back.
You see the same sophistication in the other system utilities. The Address Book, iCal, and Mail apps are well-integrated, and your system information -- even your log-in photo, if you take one -- is automatically synced across all of these.
Stability: A big reason I moved to the Mac was OS stability, which admittedly is more about user experience than user interface. The Mac OS rarely crashes, and it recovers much better when apps freeze. You can even restart the Finder without taking down the OS. My experience is that Windows not only crashes more often, but it also more often needs a full reboot. I can’t tell whether Windows 7 is more stable than Vista yet, as stability only reveals itself over time. The Mac, however, doesn't offer the same registry madness that Windows does, so it seems to resist corruption better.
Where Windows 7 beats the Mac OS X UI
Gadget sidebar: My favorite aspect of the Windows 7 UI is in fact a carryover from Vista: its gadget sidebar. With Windows 7, however, the sidebar is no longer displayed automatically. As such, your desktop is no longer partly obscured by "gadget" utilities that, quite frankly, you won't use often. Instead, you can toggle the gadget sidebar when you want it -- just as you can with Mac OS X. And you can drag them out of the sidebar and let them free-float where you want. The big difference is that Mac OS X's sidebar equivalent covers your entire desktop, rendering everything else inaccessible, and the individual gadgets can't be pulled out of that covers-everything sidebar. The Windows 7 approach to gadgets shows the kind of elegance and simplicity that Microsoft needs to do more often.
Network and Sharing Center: Windows 7's new Network and Sharing Center provides a worthwhile visual cue as to your network's setup. It also includes straightforward setup tools to diagnose the network and switch location-specific configurations. Although it is easier to actually connect to other Mac users in Mac OS X than it is to connect to other PC users in Windows, the latter provides a better overall picture of your network state than the Mac OS does.
Window resizing: Another plus for Microsoft, Windows has long let users resize application and other windows by dragging any side. Mac OS X still forces you to use the lower-right corner, which the Dock sometimes obscures.