If you have a valid ESTA you will not be required to re-register after the introduction of the fee.
No. If you have a valid registration under ESTA, you will not be required to re-register on September 8, 2010 when the fee is introduced. A regisration under ESTA is valid for two years from the date it is authorized or until the date on which the traveler’s passport expires, whichever comes first. You will be subject to the new fee, however, if your registration expires and you re-register on or after September 8, 2010.