Mine too ... although I did finally break down and buy my first ever set-top DVD player two days ago.
I have backed up over 120GB of data with my PX712a and every time I've retrieved data from DVD there have been no problems. I've used Memorex/Ritek R3, Maxell/TYG01, Maxell R002, Maxell/Ricohjpnr01, Fujifilm/Yuden000 T02, and Ritek-RiData/Ricohjpnr01, and Verabatim/MCC03 ... all with excellent results, both scanned and real-world.
Does anyone have further suggestions or media recommendations to bring this up to a very solid 100% reliability?
Passing the diagnostic self-test just means your drive isn't dead on arrival (DOA). If you could run some PIPO Sum-8/Good Accuracy scans in Plextools and then post the results here, someone here could interpret the quality and help you come to a decision as to what to do next. In your post, please also mention the media used (with media code) and the speed you burned it at.
Good luck ... if the drive produces poor-quality scans, the worst that can happen is that you have to RMA it back to Plextor. BTDTBTTSAPATC (been there, done that, bought the t-shirt, and puked at the concert)