Just one point to note from your comments, that the buffering is camera related as well as related to the write speed of the microdrives. As you may well realise, the microdrives work in the same way as 'conventional' disks used by mainframe computers (and PC's for that matter) in that the disc itself is rotating at very high speed and the writing arm or 'head assemble' is actually suspended above (but not touching) the surface of the disc. Hence, because of the physical nature of the assembly, (i.e. the disc has to spin and the head move across the radius of the disc) then the writing process will be slower compared to solid state devices like CF cards.
As I say though, the camera itself is resonsible for the buffering and will stop allowing photos to be taken as soon as it's internal buffer is full (which is then related to how quickly data can be written to the storage medium).
I notice you mention the D1. I use a D1X and the RAW format in that camera is 7.7.mB and so buffering occurs much sooner but in my case, as I do not indulge in sequence photography too often, it's quite acceptable.