As you may or may not know I am currently the owner of a new Mac Mini (Core Duo FTW!). Despite the fact that Windows is easily installed thanks to the magic of Boot Camp, I've been working in OS X mostly. I feel I've been using it long enough to give my opinion:

Pros

• Easy to use. Once I figured out the basics I pretty much got it.
• Stability (for the most part). A few minutes ago Safari died an ugly death on me dragging the rest of the system down with it and I've been in a must reboot situation twice (not including the system updates)
• Pretty looking. Hey, what can I say? I'm a sucker for the genie effect.

Cons

• Apple's interface guidlines tend to make apps overly simplistic. Toolbars are almost non-existant, everything seems to revolve around a drag and drop interface. This is an area where Windows apps can really shine given a developer who knows what they are doing.
• Keyboard craziness. I don't know about you, but I use the Home and End keys to navigate through text boxes all the time. Albiet, it's still there (Cmd-Left and Right respectively), but pressing two keys (or three if I want to make a selection) is a lot harder. Also, they seemed to ignore the delete key as well. I'm not a mouse person and I don't want to drag my effin' files to the trash. I want to press delete (and Enter to close the resulting dialog box).
• Unix directory structure. Windows can be incredibly clean in directory structure if done right. Unix is much, much more difficult and half the folders you can't see anyways. Also, mountpoints drive me nuts (although, OS X seems to keep track of all that fairly well).
• Finally, hardware support. They tell you "it just works" but that's a lie. There are no drivers for my scanner (forcing me to use a piece of shareware), minimal support for my printer, NO support for my flash drive just to name a few. Driver support is something people complain about in Windows, but I have never, EVER had a problem with hardware in XP.

So, now that I'm through with that I'll deliver my verdict: Windows XP SP2 is the best OS ever (and I've used Vista so I can rule that one out). That said, OS X is definitely the best flavor of Unix I've ever seen and I can get along with it nicely.