The today released software-update makes the IPhone a remote control for AppleTV and Macs. You can control Music and Videos from wherever you are in your flat.
Arguments: Using the IPhone as the central controlling device for music or movies fits perfectly in the living-room-entertainment-strategy that apple follows with Apple TV. The Difference to existing remote controls (see "Current Development") is the bigger touch-screen and therefore better interaction-possibilities. For Example you can easily scroll through your cds, what is not possible with other devices.
Moreover because the IPhone has no fixed buttons, the interface can be adapted to such new application-areas...
Questions: What other application areas can you think of? You could also control other devices in your household, for example the heating or the oven also from outside your house. Would that be reasonable or rather useless technological gimmicks?
Current Development: Patent from apple to use the IPhone as a remote control
Salling Clicker remote control of Itunes on a Nokia
Salling Clicker - Control computer-applications from your mobile phone. With this application it's possible to control ITunes like if you had it on your mobile device! For example you can also see CD-Artwork etc. directly on the mobile phone! (try it for free, you'll be impressed)
I think it makes absolutly no sense to control my entertainment system or other devices in my flat from outside. To get your rooms ready and warm wehn you're comming home, there are timers for, everithing else makes just security problems.
«Why do you close & lock your door? - your home system let's me in at every time»
But these security-problems already exist when you control your entertainment-system by bluetooth. Your neighbour could control your entertainment system, as soon as he hacked your authentication key.
To prevent a hack, you need to be authenticated. That could be done by the SIM-Card. To use an analogy: You're also not afraid, that someone uses GPRS and it gets billed to you, do you?
I guess where there is a need for something, there will be a product. I'm sure there are people who'd like to come home from work and find their oven already heated-up. The oven should heat up as soon the person leaves the workplace. But it might not be possible to set the timer in the morning, because you don't know in the morning when you are returning from work in the evening...