Its advantage over Windows 98, NT, XP is clear: Unix applications, unlike Windows applications, don't crash the system when they crash. Windows 98, NT, and XP simply allow applications too much access to the operating system so that, when they crash, they often drag the OS down with them.
That is certainly true about the Windows 9x product line (95, 98, and ME); there was no Ring 0 / Ring 3 distinction (well there is, but it's limited because of the 16-bit programming used in parts of 9x inherited from DOS).
Technet lists some important differences:
- NT-based OSes support multi-processors.
- NT is a true 32- and now 64-bit OS, whereas 9x contained 16-bit code in the kernel.
- NT supports specific security descriptors at a kernel level, including file system security
- NT provides per-process shared memory mapping
The inherent instability of Windows was pretty much absent from the NT line, which is why I've been using NT since Windows 2000 (when it became viable for a gamer).
As far as Win7 goes, I use it at work and at home. I dual-boot with OS X in both environments - at work I have a MacBook Pro, and at home I have my iMac.
From a usability perspective, I like Windows far, far better. I just don't understand Mac fans' attachment to their desktop environment. They do have some pretty cool animation capabilities with Cocoa, but things like only being able to resize windows from the bottom right corner drives me crazy. Not being able to Cmd+Tab to a specific top-level window, just to an application, drives me crazy.
And of course, I program in .NET. All of the Mac guys at the office prefer to code in Visual Studio whenever possible - the programming environment is definitely awesome.
It may surprise you to learn that WinNT and later support a POSIX environment. With
Subsystem for UNIX-based Applications, you can get UNIX-specific services on NT-based systems, including normal POSIX calls, case-sensitive file system support, and I think ksh, among other things. As someone who doesn't really use UNIX, I can't tell you what all it comes with.
With regard to boot-up times: I start both OS X and Win7 off of an SSD on my iMac. Their start up times are comparable (in fact, I think Windows starts faster on my iMac). On my MacBook, startup times for Windows are a bit slower, but when you consider all of the development services I have that start when I log in (like SQL Server)... I think they're pretty even. The difference between Vista and OS X was much more pronounced.
[edit]
One thing I do recognize as a big advantage of Mac over Windows is that Apple is not beholden to umpteen thousand vendors correctly writing drivers for OS X. Apple strictly controls the systems on which OS X can run, and so the systems generally appear "more reliable," because they're not really out "in the wild" like Windows systems are.
