I'm thinking of using an Arduino for my first micro-controller project; the idea is to have rule-based control over a servo motor, which in turn will move the handle on an old-school thermostat. I know it's not the most elegant solution but it will be fun
That said, in my garage, a P.O. wired up 120vac straight through the old 1970s-era bimetalic strip mechanical switch. I found that out after removing the cover and unscrewing the faceplate. I was really glad I didn't go probing at anything first!