Downsides of Mac
Downsides of an Apple Mac (PC) computer.
Poor quality operating system
Mac OS X is extremely slow. You may not notice it because it keeps putting effects while it's doing something, but if you pay attention you'll notice there is a long gap before and after these effects and every day operations, such as opening applications, It is by far the slowest operating system I have ever used.
Not as secure as Linux. There have been reports of malware getting in Mac OS X.
Logged in user switching is not enabled by default and when you try to enable it it gives a warning to do with security if this is not a secure room. Linux allows fast user switching securely whether or not your computer can be accessed by others.
What is with having both a menu bar and a task bar? It's just not that great a UI.
3D desktop "cube" effect only works for changing users (which is considered to be insecure, see above). Linux Compiz Fusion, which admittedly is not available in most distributions, has many, many more and more impressive enhanced desktop effects.
Why does it even have these problems?
These shortcomings might night seem that great on their own, but considering that Linux is free, and they could have just made a copy of it to call Mac OS X (they still can), it really makes no sense that Mac OS X has any shortcomings compared to Linux at all.
Poor quality hardware build
Poor quality external hardware parts (peripherals)
Extremely high price
An Apple computer isn't even a good computer when you put Linux on it. They are too poorly built.