Nikon D300 Complete Manual page 106

D300 to be doing two things at once (take another picture
while handling the data for the previous one).
Note: The D300 can lose images. When you turn the camera off it
may still be writing images from the buffer to the storage
card. The green indicator light stays lit to indicate this—in
other words, while you turned the camera off it is smart
enough not to actually listen to you until the buffer is
empty. But if you take a CompactFlash card out of the
camera while that indicator light is lit, you'll not only lose
some images, but you could corrupt the formatting of the
card, potentially losing all the images on the card. So make
sure the light is off before removing cards.
Tip: Here's one not many D300 shooters know about: you can
clear the buffer! This is done by holding down the Delete
button (the trashcan: p) while turning the camera off. The
camera will finish writing the current image (so that it
doesn't corrupt the card formatting) then purge the rest of
the images in the buffer.
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 106