I travel the the US from the UK on the VWP regularly. You have to register with ESTA and are supposed to update your registration before each trip with a new address. The immigration officials are completely ignoring ESTA for the time being - you still have to fill in the green form, which is what they will base your entry on. At some point it may cut over, but for the time being you have to do both.
Make sure therefore that you keep a note of your ESTA number.