I've got a mac (they gave it to me at work) and several PCs. I've found out it looks nice and has lots of eyecandy for the everyday user. It's also good for doing music and general home movie editing and photoshop stuff, and it has lots of dumbed down software for the average family.
For everything else it's a piece of hardware that looks REALLY good and costs thrice as much as a real computer (but people will think you're hip and rich and they'll worship you, I saw that in advertisements). My day job involves 3D animation and HD video creation and editing stuff. Macs with same specs than PCs, particularly those with (supposedly) the same GPU take longer for everything. Their GPUs are somehow crippled not to deliver their full power, so guys working in 3D programs get frustrated when they see someone else on a 'crappier' machine getting things done waaaaaay faster. But I know people that spend their money on them will always find ways to feel better with their choice ("it's a feaaaatureee" they'll say, and proceed to add: "it doesn't get malwareeeee and looks betteeeeer"). I think they call it emotional investment or something

.
Yeah, they don't get BSOD, they just get the rainbow colored spinning whatchamacallit stuck in an endless loop or get the software quit unexpectedly, but there are mac lovers that will tell you that's somehow a feature.
I hate the mac I got assigned at work, I only use it for simple things -computing-power wise, mind you - like vector design and photoshop. For everything else I use my Win7 powered machine, same at home. And I've yet to experience a single crash since I use the Win7 OS. But anyway, if you use it for IM you can always install some kind of emulator to run the tools of the trade, and imagine you're running them on a real PC at full speed.
http://imageshack.us/photo/my-images/840/feelathomermr.png/