Please can anyone confirm---if you fill in an ESTA form online and get authorization you don't need to do anything but turn up at check in from then on until the authorization expires. I think.
You complete the ESTA online. Once you're given the all clear, that's you cleared to fly to the States for 2 years, or until your passport expires, whichever is sooner.
You may still need to fill in an I-94W, but I believe this is now being phased out.
Obviously, each time you fly you can update your ESTA with new flight numbers and first night accommodation details, which is somewhat easier than filling out a whole new I-94W...