I use a PX-708UF2, and it works fine - does everything I need it to. Just because a new firmware version is released does not mean it should be applied. I have no intention of even looking for it. If it ain't broke, - don't fix it.
Here are Plextor's wrods on firmware upgrades:
"If you are experiencing a drive problem after updating the drive firmware, for those drives with the self-diagnostic feature (PX-320A, PX-W4012A/U, PX-4824A/U, PX-W4012S, PX-W5224A, Premium, Premium-U, PX-230A, PX-708A/UF, PX-712A/UF and PX-716A/UF/SA), please perform the self-diagnostic prior to calling Tech Support. The self-diagnostic must be performed with a disc from your drive's recommended media list. Please check your Users Manual (or download the manual) for the correct procedure."
Run the Self-Diagnostic Procedure.