I've been running this system for over a year now, it's evolved lots, but I've found it to be rock-solid. It delivers great quality audio throughout the house, and it's been lots of fun building and using it. Most of my focus has been on building the web/mobile UI software, but here are the details about the rest of the set-up: https://medium.com/@zefer/my-diy-multi-room-music-system-e65068398c63
The server chassis build was inspired by Tobias's fantastic post, here: http://support.hifiberry.com/hc/en-us/community/posts/201843381-Small-media-player-with-squeezelite-slave (Thanks!).
The next project I have in mind is to build wooden wireless remote controls. A Pi Zero, with a 16x2 LCD, a handful of buttons, a WiFi dongle and a battery.