WiFi problems on Yosemite
The latest OS X 10.10.4 public beta, build 14E26a, totally gets rid of discoveryd. Go to this Apple link and sign up for the public beta program, where you'll be given a link to download a piece of software that'll get the App Store to pick up beta updates. Take a backup of everything, install Beta Access Utility, and then install and enjoy a discoveryd-free Yosemite!