The Pioneer 108 should be one of the best writers available today, together with
the NEC35x0 and the BenQ 1620. (=my top 3)
I also have the Pio108 and the LiteON 811 : neither of them is recommended
for making valid scans : my 811s gives ALWAYS bad scans (PIE >400-1000).
The Pion 108 also gives completely different results when used for scanning (much worse) than my LiteON 832s, Benq 1620 or my 2 Plextors PX-712.
You shouldn't be worried too much about your bad scans : just test a pioneer burned disk with a 2 or 3 serie from LiteON (models xx2 or xxx3) or use a Benq or a Plextor for scanning.
current DVDRW ODD's :
16x : Pioneer DVR-108 (1.14 >NIL), Philps 1640P (Benq fw B7T9), NEC-3500AG (LDv2_beta2)
12x : 2x Plextor 712A (1.05) , LG GSA-4120 (A102)
8x : NEC2510 (Herrie 1.07v2b5) , Pioneer DVR-107D(1.18 >NIL), Sony DRU-700A (CG3E), LiteON 811 (HS0R)
4x : Sony DRU-500A (2.1a) , Pioneer DVR-106D, LiteON 411 (FS0K)
2.4x : HP200i, Ricoh MP5125A (+R/RW only)