I think something which would be insanely useful for people in cold climates like myself would be to have a unit that could learn the RF signal from a remote car starter or similar device... then have it be able to transmit that signal.
Coupled with perhaps a Macro or a timer (and maybe a temperature sensor?) you could have it automatically start up your car in the morning.
I have a car starter, but often in my morning daze forget to start the thing ahead of time to get it warmed up. (And my car takes a long time to warm up.)
Most car starters have a 'safety' setting so that if the car is started and you don't get in after a half hour or so, it will turn off automatically. So the risk is pretty low.
This could also work for hot climates I would suspect. Have your car turn on automatically and start blasting A/C to get the temp down.
I figure if I sacrifice my spare car starter, I could build this myself with one of the plug in appliance switches and a very basic circuit board... but who wants to do all that work?