There's so much tosh spouted on here I wouldn't even know where to start, you'd have thought IT type people would be less inclined to take the report from an uneducated non-specialised bunch of MPs as gospel truth.
The PAC report assumes 2% savings, the aggregated savings from over a 100 independent trials of smart meters with home displays has shown an average saving of over 9% over a number of years (with no creeping up usage again).
You will NOT get 2 home displays, every house will get a smart gas and electric meter, this will send data to a comms hub. One home display will connect to the comms hub (the hub will also send reading data to the supplier too). If you want you will be able to connect other devices to the hub (smart phone, shock! Etc).
If people actually want to make an informed decision have a read around, don't just assume that because a bunch of art graduate MPs say something it is true...
On meter life... The gas smart meter will have a battery which will easily last 10 years as it's just doing a zigbee connection to the comms hub. The electricity meter will, surprisingly, be fine since it has, ermm, electricity.