once month ago i asked if using a IBM microdrive would reduce the battery life on a d30. Well, since a microdrive uses moving part the theoretical answer was "yes"
since then i bought a microdrive, and my opinion on this it that using a microdrive reduces the number of shot that can be taken with a battery fully charged by approximatively 20% (compare to a 128MB cf Card)
I plan to make some real tests (by curiosity) (exact number of picture taken in controlled condition) but if someone already has spend sometime on it!!!