If you need to port your application to Mac OS X Yosemite, this case study by Git Tower is worth reading. http://git-tower.com/blog/tower2-yosemite-design
App Design on Yosemite
Mac OS X has hit the streets with its latest version – and so has Tower 2. We've invested countless hours to fully adapt to Yosemite's new design language. Read about what it takes to make an app feel really at home on Mac OS 10.10.