I can't blame Apple for changing the connector if we're honest, there was a serious packaging floor!
I would imagine at £25 the adaptor will be the bees knees, and will allow you to control the iphone from the car.
I'm in the same boat, i get my 5 tomorrow.
Unfortunately, you cannot control your phone music through the stereo controls when connected through Bluetooth...you have to choose on the phone (with the exception of pressing 'next/preious' track button)
However, on the off chance the adaptor from Apple doesn't allow you to control the iPhone from the stereo, I imagine that it won't be long before one of the Korean/Japanese eBay specials does allow you to!