There is definitely a market for home automation and the like, but currently costs are high.
For example, Sonos home audio systems carry a very high price tag, yet many readers here could 'roll their own' at a fraction of the cost using Homeplugs and Tri-path amplifiers (okay, the end result might not be as 'polished', but the BOM is similar).
You don't have to suffer from full-blown OCD to sometimes have a nagging feeling "Did I turn the iron off before I left the house?" as you're on your way to work. A system that could provide such confirmation through one's smartphone would be welcome. The devil will be in the ease of use in the application.
Sensors are cheap, processing power is cheap. Using an array of microphones could allow the movement of people in a house to be tracked.... turning on lights is one application, burglar detection another.... or even "There hasn't been a sound from Granny's house for 10 hours, let's give her a ring and see if she's okay".