I use my home PC for gaming, now lets ignore the fact that games are made for windows (I don't like windows either but a Mac is no PC alternative) which is a money issue (MS throwing money at publishers to use DirectX).
We have a marketing division in the company I work for that uses Mac's and I'm the admin for that division so I know what can go wrong with these machines. They are pretty much designed for the niche market of graphic designers and this is reflected in the limited amount of software available for them.
The Macintosh is really a poor platform for gaming or pretty much anything besides writing emails graphic design and browsing the web. Gaming tends to push hardware to their limits which has two effects that make Macintoshes really unsuitable, the first being that you cant upgrade the hardware yourself, the HD, Optical drive and processor are sealed. You also have no choice in what you can upgrade to, only what Apple allows. I am aware if you buy the AU$5000 Mac Pro you can open it like an ordinary PC, but I shouldn't have to spend AU$5000 for that feature.
The first being that Hardware breaks, this is a given no matter what platform you are using. The problem with this is that you cant change the hardware yourself in a Mac (specifically Imac), you need to send them to an authorised Apple service centre to be serviced with Authorised Apple parts. out of the 5 Mac's we've had in production, 3 have broken, 1 G3 had to be retired, one G4 Imac suffered a HDD failure and had sent away to be repaired (took 2 days for a 5 minute job) and another G4 Imac had a PSU blow up (wouldn't have happened if the user shut down his machine over the weekend like I told him to) this took 4 days to fix because the service centre had to order it in (there should have been a spare on the shelf). A PSU should take no more than 1 hour to install in a desktop PC and this includes the time needed to drive to the shop and buy one.
Mac's are quiet limited in what they can do and now are suject to moores law that same as Windows/Linux boxes. Also they are still more expensive, my gaming PC cost AU$1900 with no OS (AMD X2 6000, 2 GB Ram, Geforce 8800 GTS) a G5 Imac cost our company AU$2800 (Core 2 Duo 2 GHZ, 2 GB Ram, Radeon X1600) Without a warranty (I built my own gaming PC which doesn't have a warranty, I insist on being fair in this test). For AU$700 less I bought a PC with was more capable than a Mac.