A homebrew device with some IGBTs controlling main voltages, controlled by an Arduino, is vastly different from a commercial product that has to pass UL/Intertek/TUV certification (not to mention FCC EMC compliance). Those certifications exist specifically to protect consumers from devices that will burn their house down.

This isn't to say that I would discourage a hobbyist from building their home automation controls. I would strongly recommend learning about designing electronics for mains voltage (creepage and clearance, grounding strategy, fuses and other circuit protection, types of transformers and how they're built (double insulated?), capacitor voltage rating|derating, ripple current ratings, lifetime vs. temperature, etc.

You can be a hobbyist and design things well, just be thorough when it's something that can set you and everything you love on fire if you do it wrong.

Here's a recent example where a guy designed an RF system (at 315 MHz) and it prevented garage doors opening in his neighborhood. He's described as an "electronics enthusiast". Thankfully, no one was hurt with this electronics misadventure. http://www.arrl.org/news/view/hams-help-trace-mystery-signal...