Ok I don't know what is going on but here is the scoop:
My 1610 is virtually useless for burining dvd's now, the light flickers a fast pace red/green when it does burn, cd's is about all it can do, dvd's just hang in Nero (latest version), but when it does burn cd's it takes much longer, like 15 min to do a whole cd at 40x.
My 1620 burns DVD's but often takes twice as long (15min as opposed to 6min when burning at 16x) its light also flicks red/green when burning at the beginning of a burn, then just flicks red.
I have also experienced hanging burns, where nero is not responding, the light on the drive is flicking red, it does not respond to the eject button, I cannot kill nero and I basically have to reboot. I just noticed as I'm writing this, I was doing a burn, its stopped responding at 11%, and I am going to have to reboot, the red light is flicking on the drive, but there is nothing I can do. Both drives have lastest firmware, they are in master/slave config, system is Pentium 2.2 GHz, windows XP SP2. I updated the firmware on my 1620 some time ago as it was an OEM and I flashed it to retail, it was working fine for weeks and them both just started acting up. I burn mostly BenQ media, rated at 8x and I burn it at 16.