I just bough a HP 640C a week ago, flashed to BBIA 1625. Burn a few and here are my results: Burn DVD+R's are excelent on MCC003, MCC004, YudenT02, CMC MAG E01, ProdiscR05, RitekR03. However like you hear, DVD+R DL sucks, very high error. Burned a MKM01 (only 2.4X support) and it freezed on my Sony DVD player. For DVD-R, the 1625 doesn't even recognize the disc.
I think this result agree with others.