I think that in terms of reliability, for a basic or inexperienced user, even right up to your entry level or higher enthusiast... a Mac is far easier to use and more stable than a PC. I'm probably going to get flamed for that but it's just true... A Mac is so much easier to use, configure, and enjoy without having to worry about all the crap that is associated with Windows.
I believe Windows requires a lot more competency to be on the same level as Mac OSX.
I would say that is true for the average user, and perhaps enthusiast for photo/video/music editing. For Gaming not so much, especially if you need to run boot camp and install/run windows anyway. The other problem I found is that because OSX basically still uses a deviate or openGL instead of Direct X, even if games are ported over to mac they tend to run poorer in the mac environment because the game is not optimized for openGL. A great example of this is SC2. I could install it on both the mac and windows side. On the mac side I could only run it at low settings while being able to maintain a high framerate, whereas on the same system but on the windows partition, I could run medium/high settings.
Don't get me wrong, I still really love the mac interface, and I used a Mac for about 4 years before I swapped back to a PC. In the end I found that I was running Windows 7 on my mac more than I was running OSX in order to facilitate my gaming. It really just depends on what you want to do with it, and what graphics settings/frame rates you are willing to run at.
On a side note, I did find that WoW actually ran about the same in both environments, but pretty much all the other games I played via steam ran better on the windows side because of directX.