UPDATE #1: Ignore my post below unless you have the same issue. It seems restarting my Mac fixed the blurry-fonts issue. UPDATE #2: Turns out that a restart simply solves the issue temporarily but eventually comes back in the same session. A more permanent fix (until this bug is eliminated by Apple Inc.) is to do as user Paradoxally stated: "Turn off LCD font aliasing under General [then restart your computer]." I can't be the only one. OS X Yosemite has turned my 27" iMac into a blurry text renderer. I feel like I need a new eye exam and glasses prescription. I have a half-solution, but it requires eliminating the transparency effect: Go to System Preferences > Accessibility Check "Reduce transparency" ...but it doesn't eliminate all of it. The sub-menus are still blurry. I may discover more. Here's an example: You'll notice the sub-menu items are blurry (under View), yet the Accessibility window underneath displays fonts in sharpness. UPDATE: Restarting my Mac fixed the blurry-fonts issue. I'll keep an eye out for it, but I hope the issue doesn't return.