My iMac. Upgrading to Yosemite was the worst mistake ever. Now I have to use a cheap mouse and keyboard, as Apple's Bluetooth versions no longer wake the sleeping iMac. I have tried every solution on the Internet to this and none fix it. The beachball is becoming ever more prominent on the iMac too. Very disappointing for a machine which isn't 3 years old.
My Macbook Air. It's better, but the power button no longer does anything when I press it.
Apple products have a huge premium and the quality of the software is not matching the price tag. I am not surprised to see the stock falling; usually when IBM buy your products en masse you know something is wrong :)
I don't know what the culture at Apple is. But I don't think their software developers can be anything other than the "norm" - and I am extremely worried about their automated testing culture. Maybe someone can comment.
EDIT: I just remembered my Apple Cr*p folder home to Podcasts, Tips, Apple Watch, Calendar, Health, Apple Store, Apple Maps, Videos, Reminders and Newstand. Podcasts actually cost me money when it started downloaded podcasts over 3G despite me saying wifi only. I think that bug got fixed, but I'll never trust it again. I also forgot about the white elephant that is the Apple Time capsule I purchased. It's slow over wifi from the iMac and was one of the causes of my beachball, but the main issue was it kept saying it couldn't back up because the disk was locked. For a company like Apple who should supposedly simplify backup, the product is a shambles. Maybe this is better now, but I won't be upgrading.