The hard drive in my 2009 iMac failed and I'm too lazy to take it to the Mac store, and too cheap to pay them inflated prices to fix it.
Super easy. The guides were really helpful, and ifixit.com is super intuitive and easy to navigate and find exactly what you need so you can be confident in doing the right thing. I have never taken a computer apart, and pulled this off without a hitch.
Just make sure you're paying attention to how things are supposed to be before you disassemble (specifically when removing parts from your beat hard drive to transfer to the new one).