Without quantitative metrics, the responsiveness is just way better than Mavericks. With Mavericks I just felt like I was waiting for it all the time, even on a maxed out laptop with SSD.

With Yosemite, even my 3 year old iMac is doing way better.

Safari has always been slow for me until this release.

The trade off is that I really hate the way Yosemite looks but I can live with the tradeoff.

Note: all my machines have 12 GB or 16GB of ram