I burn at 1/4 the maximum speed my drive allows because in my experience although *some* DVDs come out okay at the maximum burn speed, quite a few do not. This is using Verbatim DVD+R (or another brand that uses the exact same manufactured disc with their label on it). So typically I burn at 4x and never experience a problem.
This was after a year or two of burning DVDs using the maximum speed, and probably four years burning CDs at the maximum speed. I had read that advice (to burn slower) but didn't heed it until I experienced it myself. If it's worth having, it's worth having at a reliable quality, IMHO.