I have noticed that turning down the laser intensity (-1 or -2 setting) with the VariRec option in Nero or Plextools yields sightly better dvd burns.
Below are some Burst test PO/PI scans from Plextools. The first scan is a burn with VariRec setting @ -2. All the other scans are of discs with VariRec turned off. Burn speed for all discs (Ridata +R 8x R03) was 4x. My drive is a 712a and I used Nero (22.214.171.124) to burn the discs.
The difference is almost negligible and since playback of all the discs are fine on my very picky laptop drive (Matshita SR-8175) it probably isn't worth it if one wants to burn at a faster speed than 4x.
I'm going to try some really crappy, and maybe some -R media in a couple of days and see if there's a difference.