i got two samsung 18x sata dvd-r drives a few days ago.
they work fine, and one benefit (yes! a benefit!) i noticed is i can be writing a cd with one drive at full 16x speed, while watching a dvd on the other, and since there's no shared bus bandwidth, there's no inteference whatsoever between the two drives, since they both have their own connection to the motherboard.
no speed difference, tho. i really just got it cause i wanted to take advantage of some of the lonely sata ports on my computer, it's just neat that there's no cross interference between the two drives, even when one drive is locked (in a writing situation)