Just read at Autosport.com that 2014 spec weight now is 690 kg, 48 kg more than the current spec. So despite ~50 kg less fuel, at the start the cars will weigh the same as 2013, but ~48 kg more at the finish.
Pirelli are anticipating the cars will produce ~900 bhp, which I take to be petrol power plus ERS combined, so I was puzzled when Charlie Whiting predicted they would be 2-3 seconds/lap slower than 2013. The increased spec weight explains it.
The last draught of the 2014 TR I downloaded lists 660 kg as spec weight. That it keeps incrementing upwards I take to mean the teams are finding the lighter weights too ambitious.