I just uploaded the obligatory back-of-the-envelope image of the candy cooker.
One of the reasons I chose a candy cooker as the first instance is that candy is cool. I have an old mercury based candy thermometer and think that having a closed loop control system would be more fun and less toxic if I mess up.
Another motivation for this project is the ease of making a working prototype.
[Full disclosure: the envelope came much later than the candy cooker concept.]