well this is exactly what happens.
i start burning an iso at 8x with dvd decrypter and the buffer goes all the way up. the lead in starts writing and the drive spins up a few times and the burning begins. then the transfer starts and the speed goes up to about 6x then drops back down to 0x. then it takes about 5 minutes before it starts up again, but now its constantly at 4x. the burn finishes fine, but the disc runs like crap and u can see the burn lines on the disc. looks kinda like the rings on a tree trunk. if i burn at 4x to begin with, it drops to about 2x and continues at 3x but never actually stops burning. the disc comes out fine, but the playback is choppy.
in some cases, when the burn speed goes to 0x, the green light on the drive just flashes non stop for a while and my whole comp crashes. i still get i/o errors once in a while telling me that it cant find the address, but a restart fixes that.