Sunny
To make my life easier, I started to use "high" quality drives but even in this case I'm not 100% happy. For instance yesterday, I couldn't get K3b to burn a DVD-R disc (DVD+RW was OK) and I had to use growisofs from the command line. Moreover, one (cheap) DVD-R disc contained a corrupted file ... Perhaps more expensive DVD discs are more reliable, I'll try it later.
Actually, this is known problem not in k3b, but in growisofs. As far as I know, it happens with Plextor and some other drives. When drive's firmware is not up to date, or not complete, and it does not recognize correctly the media, it can return some bad formated speed settings, which in turn are used from k3b. Usually it happens with -R disks.
Firmware upgrade of my Plextor PX-712A (from V1.03 to V1.05) didn't fix the problem with K3b. I'll investigate the problem later. -- A.M.