I think Plextor quality started suffering sometime after they went from an all-SCSI-all-the-time company to the IDE crowd.
I have a Plextor 40X Max and a Plextor 12x10x32x burner on a basic Adaptec SCSI card in my wife's system, and those are still working great. I think they cut corners trying to bring drive price down closer to other manufacturers as the market has become more cutthroat, but their prices are still higher, and yet I can get a better quality drive from NEC or Pioneer.
The only thing they offer above others is their SATA burners, but that's slowly changing (MSI has one I believe, and a few others are projected for the future by Benq and others).
Intel Q9450 @3.2GHz, Gigabyte GA EP45-UD3P, 4 x 2GB G.Skill @4-4-4-12
Antec P160SW case (modded), Xigmatek 750w PSU
3x 500GB (RAID-5), , OptiArc 7200S, ASUS E818A3T
Creative X-Fi XtremeGamer, Hauppauge HVR-1800, Radeon 4890