Over on the Mac mini forum, I shared my experience with running Yosemite on my Mac mini (Early 2009). I ran benchmarks that proved the UI is drastically slower in Yosemite compared to previous versions of OS X. Well, at least on my machine anyway The whole OS feels very unresponsive, most evident in the simple act of resizing a window. Something which we have been doing since the 80s. Here's my experience. I have 4GB of RAM, SSD and a clean install. It's just a Finder window showing some folders. Nothing complex at all. Resizing a window in Mavericks: http://youtu.be/174ugKsj6z4 Resizing a window in Yosemite: http://youtu.be/1TMh5Pjj4uk Core Animation in Yosemite must have taken a fundamental change because something strange is afoot. Is everything vector now? I would love to know if others have experienced such a hit in UI responsiveness or have any idea what Apple have done under the hood that has caused this?