I think there are lot of useful cases, but I don't think voice control would be useful however (nobody wants to have a conversation with their microwave).
Lighting automation would be useful in a number of ways; on\off\vacation schedule, see a list of all active lights with power consumption (and then turn them off remotely), auto on\off depending on your location, etc...
Appliance automation; coffee pots have timers but why not control the settings from your remote device? Preheat the oven remotely, schedule your slow cooker based on your schedule, notifications when timers are done (microwave, oven, washer, dryer, etc...)
Power Monitoring; get a detailed report on power consumption per appliance, room, season and setup automation depending on peak hour usage rates.
Audio\Video: Crestron has some great automation, Logitech has excellent remotes, imagine if you could control the lights when settling in to watch a movie.
Security; get live feeds from your house, pickup audio, two way communication, remotely control locks (real security concern here however), random light control when on vacation.
All of these things can be done but are not integrated. If all these devices worked together we could think of some really creative ways to automate, making a phone or tablet the central control device for the home would be genius!