Remote controlled wall plugs
In our house we are controlling all of our lights (And some other stuff) using remote controllable wall plugs that are switched using radio frequency. We have them hooked up to a home automation system(Telldus) that manages when they should switch On or Off. The absolutely most frustrating thing about using these wall plugs have been their size.
In many cases when you have put one of these in a two way electrical socket you have blocked the other one for proper use. Especially if you are trying to fit a very bulky AC adapter in the other socket.
The new generation of these wall plugs are a lot slimmer! They can handle more load (≈ 250% increase) then the predecessor and there is also a version available that can monitor the energy consumption (At a higher price though). The new generation comes with a very modest price increase of ≈ 2 EUR. Now that is good product development!