What frustrates me most in the recent time is the wall of bugs I face in Mac OS X and Safari particularly. It is getting so ridiculous that even some Apple-pages do not work in Safari for me, s.t. I have to switch to Chrome to get the content. For example, opening this URL:
http://support.apple.com/kb/PH18686?viewlocale=en_US
results in just a white page in the latest Safari on Yosemite.